elaine newman | Concordia University (Canada) (original) (raw)

Papers by elaine newman

Research paper thumbnail of The leucine/Lrp regulon: A new example of global regulation in Escherichia coli K-12

Research paper thumbnail of Identification of Lrp-regulated genes by inverse PCR and sequencing: regulation of two mal operons of Escherichia coli by leucine-responsive regulatory protein

Journal of Bacteriology

We have used the technique of inverse PCR to identify Escherichia coli chromosomal genes carrying... more We have used the technique of inverse PCR to identify Escherichia coli chromosomal genes carrying Lrp-regulated inserts. This technique revealed that malT, malEFG, and malB-lamB-malK are all activated two- to fivefold by Lrp and confirmed that Lrp regulates expression of the leuDBCA and livHJKG operons. lacZ transcription is also increased in the presence of Lrp. However, the growth rate of the Lrp mutant on maltose and lactose is not decreased by Lrp deficiency.

Research paper thumbnail of Structure of the Lrp Regulated Promoter of E. coli K12

Research paper thumbnail of How much territory can a single E. coli cell control?

Frontiers in Microbiology, 2015

How much territory can a single E. coli cell control? Front. Microbiol. 6:309. Bacteria have been... more How much territory can a single E. coli cell control? Front. Microbiol. 6:309. Bacteria have been traditionally classified in terms of size and shape and are best known for their very small size. Escherichia coli cells in particular are small rods, each 1-2 µ. However, the size varies with the medium, and faster growing cells are larger because they must have more ribosomes to make more protoplasm per unit time, and ribosomes take up space. Indeed, Maaløe's experiments on how E. coli establishes its size began with shifts between rich and poor media. Recently much larger bacteria have been described, including Epulopiscium fishelsoni at 700 µm and Thiomargarita namibiensis at 750 µm. These are not only much longer than E. coli cells but also much wider, necessitating considerable intracellular organization. Epulopiscium cells for instance, at 80 µm wide, enclose a large enough volume of cytoplasm to present it with major transport problems. This review surveys E. coli cells much longer than those which grow in nature and in usual lab cultures. These include cells mutated in a single gene (metK) which are 2-4× longer than their non-mutated parent. This metK mutant stops dividing when slowly starved of S-adenosylmethionine but continues to elongate to 50 µm and more. FtsZ mutants have been routinely isolated as long cells which form during growth at 42°C. The SOS response is a well-characterized regulatory network that is activated in response to DNA damage and also results in cell elongation. Our champion elongated E. coli is a metK strain with a further, as yet unidentified mutation, which reaches 750 µm with no internal divisions and no increase in width.

Research paper thumbnail of Role of L-threonine dehydrogenase in the catabolism of threonine and synthesis of glycine by Escherichia coli

Journal of bacteriology, 1976

The enzyme L-threonine dehydrogenase was demonstrated in extracts of Escherichia coli K-12, and w... more The enzyme L-threonine dehydrogenase was demonstrated in extracts of Escherichia coli K-12, and was shown to be the first enzyme of the pathway converting threonine to glycine. The enzyme was induced by L-leucine, but not by its substrate, L-threonine. The metabolic significance of leucine as a catabolic signal for amino acid degradation is considered.

Research paper thumbnail of A novel L-serine deaminase activity in Escherichia coli K-12

Journal of bacteriology, 1991

We demonstrate here that Escherichia coli K-12 synthesizes two different L-serine deaminases (L-S... more We demonstrate here that Escherichia coli K-12 synthesizes two different L-serine deaminases (L-SD) catalyzing the nonoxidative deamination of L-serine to pyruvate, one coded for by the previously described sdaA gene and a second, hitherto undescribed enzyme which we call L-SD2. A strain carrying a null mutation in sdaA made no detectable L-SD in minimal medium, but had activity in Luria broth. We describe a mutation, sdaX, which affects the regulation of L-SD2 and permits its expression in minimal medium, and an insertion mutation, sdaB, which abolishes L-SD2 activity completely. Both mutations lie near 60.5 min on the E. coli genetic map. The two L-SD enzymes have similar enzyme parameters, and both require posttranslational activation.

Research paper thumbnail of A single mutation affects L-serine deaminase, L-leucyl-, L-phenylalanyl-tRNA protein transferase, and proline oxidase activity in Escherichia coli K-12

Journal of bacteriology, 1978

A mutation at a single locus, wyb, results in several phenotypic changes in Escherichia coli K-12... more A mutation at a single locus, wyb, results in several phenotypic changes in Escherichia coli K-12. The Wyb- phenotype includes: (i) an increase in L-serine deaminase activity, together with a loss of inducibility by L-leucine; (ii) an absence of L-leucyl-, L-phenylalanyl-tRNA protein transferase activity; (iii) inducibility of proline oxidase by proline; and (iv) a loss of ability to use maltose as a carbon and energy source.

Research paper thumbnail of Role of threonine dehydrogenase in Escherichia coli threonine degradation

Journal of bacteriology, 1977

Threonine was used as nitrogen source by Escherichia coli K-12 through a pathway beginning with t... more Threonine was used as nitrogen source by Escherichia coli K-12 through a pathway beginning with the enzyme threonine dehydrogenase. The 2-amino-3-ketobutyrate formed was converted to glycine, and the glycine was converted to serine, which acted as the actual nitrogen donor. The enzyme formed under anaerobic conditions and known as threonine deaminase (biodegradative) is less widespread than threonine dehydrogenase and may be involved in energy metabolism rather than in threonine degradation per se.

Research paper thumbnail of Map location of the ssd mutation in Escherichia coli K-12

Journal of bacteriology, 1980

A pleiotropic mutation at the ssd locus was mapped at 86 min near rha. A mutation at the ssd locu... more A pleiotropic mutation at the ssd locus was mapped at 86 min near rha. A mutation at the ssd locus resulted in elevated L-serine deaminase activity, inability to grow with succinate as the carbon source, and inability to grow anaerobic conditions.

Research paper thumbnail of Control of nitrogenase in a photosynthetic autotrophic bacterium, Ectothiorhodospira sp

Journal of bacteriology, 1982

An Ectothiorhodospira species fixed nitrogen when grown as an autotroph in completely inorganic m... more An Ectothiorhodospira species fixed nitrogen when grown as an autotroph in completely inorganic medium by using a variety of electron donors. The organism also used organic carbon sources; however, this required induction of synthesis of various enzymes, whereas the enzymes needed for autotrophic growth were synthesized constitutively. Nitrogenase induction and function were inhibited by ammonium chloride. Nitrogenase activity was dependent on light and inhibited by oxygen.

Research paper thumbnail of L-Serine deaminase activity is induced by exposure of Escherichia coli K-12 to DNA-damaging agents

Journal of bacteriology, 1982

The synthesis of L-serine deaminase in Escherichia coli K-12 was induced after exposure of cells ... more The synthesis of L-serine deaminase in Escherichia coli K-12 was induced after exposure of cells to a variety of DNA-damaging agents, including UV irradiation, nalidixic acid, and mitomycin C. Synthesis was also induced during growth at high temperature. A mutant constitutive for SOS functions showed an elevated level of L-serine deaminase activity. The response to DNA-damaging agents thus may be mediated via the SOS system.

Research paper thumbnail of L-serine degradation in Escherichia coli K-12: a combination of L-serine, glycine, and leucine used as a source of carbon

Journal of bacteriology, 1982

Escherichia coli K-12 strain CU1008 cannot use L-serine as the sole carbon source, but it could u... more Escherichia coli K-12 strain CU1008 cannot use L-serine as the sole carbon source, but it could use L-serine as an auxiliary carbon source with glucose, L-alanine, or pyruvate and could derive energy from L-serine to support oxygen uptake. CU1008 grew with L-serine if it was also provided with glycine and leucine. These may act by increasing the available activity of L-serine deaminase; other explanations are also explored.

Research paper thumbnail of L-serine degradation in Escherichia coli K-12: directly isolated ssd mutants and their intragenic revertants

Journal of bacteriology, 1982

Two methods for the direct isolation of spontaneous ssd mutants of Escherichia coli K-12 strains ... more Two methods for the direct isolation of spontaneous ssd mutants of Escherichia coli K-12 strains are described; (i) by growth with L-serine as the carbon source, and (ii) by low-level kanamycin resistance. A newly isolated mutant had the same phenotype as the mutant described previously, including inefficient use of the glucose, inability to growth with succinate, altered transport characteristics, and altered resistance to certain growth effectors. Succinate-utilizing derivatives which appear to be intragenic are characterized in detail. The relation between the mutants isolated here and mutants which are thought to have impairment in a system of coupling respiratory energy to active transport (ecfB mutants) is discussed.

Research paper thumbnail of Threonine as a carbon source for Escherichia coli

Journal of bacteriology, 1981

Threonine can be used aerobically as the sole source of carbon and energy by mutants of Escherich... more Threonine can be used aerobically as the sole source of carbon and energy by mutants of Escherichia coli K-12. The pathway used involves the conversion of threonine via threonine dehydrogenase to aminoketobutyric acid, which is further metabolized by aminoketobutyric acid ligase, forming acetyl coenzyme A and glycine. A strain devoid of serine transhydroxymethylase uses this pathway and excretes glycine as a waste product. Aminoketobutyric acid ligase activity was demonstrated after passage of crude extracts through Sephadex G100.

Research paper thumbnail of Studies on L-serine deaminase in Escherichia coli K-12

Journal of bacteriology, 1974

l-Serine deaminase has been studied in toluene-treated cells of Escherichia coli K-12 and shown t... more l-Serine deaminase has been studied in toluene-treated cells of Escherichia coli K-12 and shown to be a discrete entity distinct from l-threonine deaminase. Its level in the cell varies as a function of nitrogen nutrition, carbon source, and amino acids (glycine and leucine). The metabolic role of the enzyme remains unclear but may be related to serine toxicity. The enzyme is unstable within the cell in the presence of its inducers, glycine and leucine, but not in their absence.

Research paper thumbnail of A mutation in Escherichia coli K-12 results in a requirement for thiamine and a decrease in L-serine deaminase activity

Journal of bacteriology, 1985

Mutants of Escherichia coli K-12 deficient in L-serine deaminase (L-SD) activity have been isolat... more Mutants of Escherichia coli K-12 deficient in L-serine deaminase (L-SD) activity have been isolated. These strains required thiamine and grew normally when it was provided. The decrease in L-SD activity caused no obvious metabolic deficiency. A study of revertants and transductants showed that a single mutation was responsible for the thiamine requirement and for the decrease in L-SD activity.

Research paper thumbnail of In vitro and in vivo activation of L-serine deaminase in Escherichia coli K-12

Journal of bacteriology, 1985

Escherichia coli L-serine deaminase (L-SD) in crude extracts made in glycylglycine could be activ... more Escherichia coli L-serine deaminase (L-SD) in crude extracts made in glycylglycine could be activated by incubation with iron sulfate and dithiothreitol. This activation could also be demonstrated in vitro in two mutants which were physiologically deficient in L-SD activity in vivo. This suggests that these mutants were deficient not in L-SD but in an enzyme(s) activating L-SD. The suggestion is made that production of a functional L-SD in vivo requires activation of the structural gene product by an enzyme or enzymes that reduce the protein to an active form.

Research paper thumbnail of L-serine degradation in Escherichia coli K-12: cloning and sequencing of the sdaA gene

Journal of bacteriology, 1989

A new mutant of Escherichia coli K-12 unable to grow with L-serine, glycine, and L-leucine has be... more A new mutant of Escherichia coli K-12 unable to grow with L-serine, glycine, and L-leucine has been isolated by lambda plac Mu insertion and shown to be deficient in L-serine deaminase activity. The corresponding gene, sdaA, has been cloned from a prototrophic strain, and the clone has been characterized and sequenced. The evidence is consistent with the hypothesis that sdaA is the structural gene for L-serine deaminase. However, other possibilities are also considered. No significant homology with previously reported DNA or protein sequences was detected.

Research paper thumbnail of The leucine regulon of Escherichia coli K-12: a mutation in rblA alters expression of L-leucine-dependent metabolic operons

Journal of bacteriology, 1990

We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the a... more We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the activity of a number of enzymes involved in different metabolic pathways, all of which are regulated by leucine. Selected for its ability to grow with L-serine as sole carbon source, the rbl-1::Tn10 mutant had high levels of L-serine deaminase activity (due to increased transcription of the structural gene) and of another amino acid-degrading enzyme, L-threonine dehydrogenase, and decreased transcription of the operons serA and ilvIH, coding for biosynthetic enzymes. The rbl mutation suppressed the slow growth of a metK mutant, deficient in S-adenosylmethionine synthetase. Furthermore, metK mutants spontaneously accumulated faster-growing rbl-like derivatives, and a commonly used metK strain, RG62, carries such a mutation. The rbl gene is located near 20 min on the E. coli genetic map. All phenotypes of the rbl mutant could be observed in rbl+ strains cultivated in the presence of L-leuci...

Research paper thumbnail of Derivation of glycine from threonine in Escherichia coli K-12 mutants

Journal of bacteriology, 1975

Escherichia coli AT2046 has been shown previously to lack the enzyme serine transhydroxymethylase... more Escherichia coli AT2046 has been shown previously to lack the enzyme serine transhydroxymethylase and to require exogenous glycine for growth as a consequence. Strains JEV73 and JEV73R, mutants derived from strain AT2046, are shown here to be serine transhydroxymethylase deficient, but able to derive their glycine from endogenously synthesized threonine. Leucine is shown to be closely involved in the regulation of biosynthesis of glycine, to spare glycine in strain AT2046T, to replace glycine in strain JEV73, and to increase threonine conversion to glycine in a representative prototroph of E. coli. An interpretation of strains JEV73 and JEV73R as regulatory mutants of strain AT2046 is given. A hypothesis as to the role of leucine as a signal for nitrogen scavenging is suggested.

Research paper thumbnail of The leucine/Lrp regulon: A new example of global regulation in Escherichia coli K-12

Research paper thumbnail of Identification of Lrp-regulated genes by inverse PCR and sequencing: regulation of two mal operons of Escherichia coli by leucine-responsive regulatory protein

Journal of Bacteriology

We have used the technique of inverse PCR to identify Escherichia coli chromosomal genes carrying... more We have used the technique of inverse PCR to identify Escherichia coli chromosomal genes carrying Lrp-regulated inserts. This technique revealed that malT, malEFG, and malB-lamB-malK are all activated two- to fivefold by Lrp and confirmed that Lrp regulates expression of the leuDBCA and livHJKG operons. lacZ transcription is also increased in the presence of Lrp. However, the growth rate of the Lrp mutant on maltose and lactose is not decreased by Lrp deficiency.

Research paper thumbnail of Structure of the Lrp Regulated Promoter of E. coli K12

Research paper thumbnail of How much territory can a single E. coli cell control?

Frontiers in Microbiology, 2015

How much territory can a single E. coli cell control? Front. Microbiol. 6:309. Bacteria have been... more How much territory can a single E. coli cell control? Front. Microbiol. 6:309. Bacteria have been traditionally classified in terms of size and shape and are best known for their very small size. Escherichia coli cells in particular are small rods, each 1-2 µ. However, the size varies with the medium, and faster growing cells are larger because they must have more ribosomes to make more protoplasm per unit time, and ribosomes take up space. Indeed, Maaløe's experiments on how E. coli establishes its size began with shifts between rich and poor media. Recently much larger bacteria have been described, including Epulopiscium fishelsoni at 700 µm and Thiomargarita namibiensis at 750 µm. These are not only much longer than E. coli cells but also much wider, necessitating considerable intracellular organization. Epulopiscium cells for instance, at 80 µm wide, enclose a large enough volume of cytoplasm to present it with major transport problems. This review surveys E. coli cells much longer than those which grow in nature and in usual lab cultures. These include cells mutated in a single gene (metK) which are 2-4× longer than their non-mutated parent. This metK mutant stops dividing when slowly starved of S-adenosylmethionine but continues to elongate to 50 µm and more. FtsZ mutants have been routinely isolated as long cells which form during growth at 42°C. The SOS response is a well-characterized regulatory network that is activated in response to DNA damage and also results in cell elongation. Our champion elongated E. coli is a metK strain with a further, as yet unidentified mutation, which reaches 750 µm with no internal divisions and no increase in width.

Research paper thumbnail of Role of L-threonine dehydrogenase in the catabolism of threonine and synthesis of glycine by Escherichia coli

Journal of bacteriology, 1976

The enzyme L-threonine dehydrogenase was demonstrated in extracts of Escherichia coli K-12, and w... more The enzyme L-threonine dehydrogenase was demonstrated in extracts of Escherichia coli K-12, and was shown to be the first enzyme of the pathway converting threonine to glycine. The enzyme was induced by L-leucine, but not by its substrate, L-threonine. The metabolic significance of leucine as a catabolic signal for amino acid degradation is considered.

Research paper thumbnail of A novel L-serine deaminase activity in Escherichia coli K-12

Journal of bacteriology, 1991

We demonstrate here that Escherichia coli K-12 synthesizes two different L-serine deaminases (L-S... more We demonstrate here that Escherichia coli K-12 synthesizes two different L-serine deaminases (L-SD) catalyzing the nonoxidative deamination of L-serine to pyruvate, one coded for by the previously described sdaA gene and a second, hitherto undescribed enzyme which we call L-SD2. A strain carrying a null mutation in sdaA made no detectable L-SD in minimal medium, but had activity in Luria broth. We describe a mutation, sdaX, which affects the regulation of L-SD2 and permits its expression in minimal medium, and an insertion mutation, sdaB, which abolishes L-SD2 activity completely. Both mutations lie near 60.5 min on the E. coli genetic map. The two L-SD enzymes have similar enzyme parameters, and both require posttranslational activation.

Research paper thumbnail of A single mutation affects L-serine deaminase, L-leucyl-, L-phenylalanyl-tRNA protein transferase, and proline oxidase activity in Escherichia coli K-12

Journal of bacteriology, 1978

A mutation at a single locus, wyb, results in several phenotypic changes in Escherichia coli K-12... more A mutation at a single locus, wyb, results in several phenotypic changes in Escherichia coli K-12. The Wyb- phenotype includes: (i) an increase in L-serine deaminase activity, together with a loss of inducibility by L-leucine; (ii) an absence of L-leucyl-, L-phenylalanyl-tRNA protein transferase activity; (iii) inducibility of proline oxidase by proline; and (iv) a loss of ability to use maltose as a carbon and energy source.

Research paper thumbnail of Role of threonine dehydrogenase in Escherichia coli threonine degradation

Journal of bacteriology, 1977

Threonine was used as nitrogen source by Escherichia coli K-12 through a pathway beginning with t... more Threonine was used as nitrogen source by Escherichia coli K-12 through a pathway beginning with the enzyme threonine dehydrogenase. The 2-amino-3-ketobutyrate formed was converted to glycine, and the glycine was converted to serine, which acted as the actual nitrogen donor. The enzyme formed under anaerobic conditions and known as threonine deaminase (biodegradative) is less widespread than threonine dehydrogenase and may be involved in energy metabolism rather than in threonine degradation per se.

Research paper thumbnail of Map location of the ssd mutation in Escherichia coli K-12

Journal of bacteriology, 1980

A pleiotropic mutation at the ssd locus was mapped at 86 min near rha. A mutation at the ssd locu... more A pleiotropic mutation at the ssd locus was mapped at 86 min near rha. A mutation at the ssd locus resulted in elevated L-serine deaminase activity, inability to grow with succinate as the carbon source, and inability to grow anaerobic conditions.

Research paper thumbnail of Control of nitrogenase in a photosynthetic autotrophic bacterium, Ectothiorhodospira sp

Journal of bacteriology, 1982

An Ectothiorhodospira species fixed nitrogen when grown as an autotroph in completely inorganic m... more An Ectothiorhodospira species fixed nitrogen when grown as an autotroph in completely inorganic medium by using a variety of electron donors. The organism also used organic carbon sources; however, this required induction of synthesis of various enzymes, whereas the enzymes needed for autotrophic growth were synthesized constitutively. Nitrogenase induction and function were inhibited by ammonium chloride. Nitrogenase activity was dependent on light and inhibited by oxygen.

Research paper thumbnail of L-Serine deaminase activity is induced by exposure of Escherichia coli K-12 to DNA-damaging agents

Journal of bacteriology, 1982

The synthesis of L-serine deaminase in Escherichia coli K-12 was induced after exposure of cells ... more The synthesis of L-serine deaminase in Escherichia coli K-12 was induced after exposure of cells to a variety of DNA-damaging agents, including UV irradiation, nalidixic acid, and mitomycin C. Synthesis was also induced during growth at high temperature. A mutant constitutive for SOS functions showed an elevated level of L-serine deaminase activity. The response to DNA-damaging agents thus may be mediated via the SOS system.

Research paper thumbnail of L-serine degradation in Escherichia coli K-12: a combination of L-serine, glycine, and leucine used as a source of carbon

Journal of bacteriology, 1982

Escherichia coli K-12 strain CU1008 cannot use L-serine as the sole carbon source, but it could u... more Escherichia coli K-12 strain CU1008 cannot use L-serine as the sole carbon source, but it could use L-serine as an auxiliary carbon source with glucose, L-alanine, or pyruvate and could derive energy from L-serine to support oxygen uptake. CU1008 grew with L-serine if it was also provided with glycine and leucine. These may act by increasing the available activity of L-serine deaminase; other explanations are also explored.

Research paper thumbnail of L-serine degradation in Escherichia coli K-12: directly isolated ssd mutants and their intragenic revertants

Journal of bacteriology, 1982

Two methods for the direct isolation of spontaneous ssd mutants of Escherichia coli K-12 strains ... more Two methods for the direct isolation of spontaneous ssd mutants of Escherichia coli K-12 strains are described; (i) by growth with L-serine as the carbon source, and (ii) by low-level kanamycin resistance. A newly isolated mutant had the same phenotype as the mutant described previously, including inefficient use of the glucose, inability to growth with succinate, altered transport characteristics, and altered resistance to certain growth effectors. Succinate-utilizing derivatives which appear to be intragenic are characterized in detail. The relation between the mutants isolated here and mutants which are thought to have impairment in a system of coupling respiratory energy to active transport (ecfB mutants) is discussed.

Research paper thumbnail of Threonine as a carbon source for Escherichia coli

Journal of bacteriology, 1981

Threonine can be used aerobically as the sole source of carbon and energy by mutants of Escherich... more Threonine can be used aerobically as the sole source of carbon and energy by mutants of Escherichia coli K-12. The pathway used involves the conversion of threonine via threonine dehydrogenase to aminoketobutyric acid, which is further metabolized by aminoketobutyric acid ligase, forming acetyl coenzyme A and glycine. A strain devoid of serine transhydroxymethylase uses this pathway and excretes glycine as a waste product. Aminoketobutyric acid ligase activity was demonstrated after passage of crude extracts through Sephadex G100.

Research paper thumbnail of Studies on L-serine deaminase in Escherichia coli K-12

Journal of bacteriology, 1974

l-Serine deaminase has been studied in toluene-treated cells of Escherichia coli K-12 and shown t... more l-Serine deaminase has been studied in toluene-treated cells of Escherichia coli K-12 and shown to be a discrete entity distinct from l-threonine deaminase. Its level in the cell varies as a function of nitrogen nutrition, carbon source, and amino acids (glycine and leucine). The metabolic role of the enzyme remains unclear but may be related to serine toxicity. The enzyme is unstable within the cell in the presence of its inducers, glycine and leucine, but not in their absence.

Research paper thumbnail of A mutation in Escherichia coli K-12 results in a requirement for thiamine and a decrease in L-serine deaminase activity

Journal of bacteriology, 1985

Mutants of Escherichia coli K-12 deficient in L-serine deaminase (L-SD) activity have been isolat... more Mutants of Escherichia coli K-12 deficient in L-serine deaminase (L-SD) activity have been isolated. These strains required thiamine and grew normally when it was provided. The decrease in L-SD activity caused no obvious metabolic deficiency. A study of revertants and transductants showed that a single mutation was responsible for the thiamine requirement and for the decrease in L-SD activity.

Research paper thumbnail of In vitro and in vivo activation of L-serine deaminase in Escherichia coli K-12

Journal of bacteriology, 1985

Escherichia coli L-serine deaminase (L-SD) in crude extracts made in glycylglycine could be activ... more Escherichia coli L-serine deaminase (L-SD) in crude extracts made in glycylglycine could be activated by incubation with iron sulfate and dithiothreitol. This activation could also be demonstrated in vitro in two mutants which were physiologically deficient in L-SD activity in vivo. This suggests that these mutants were deficient not in L-SD but in an enzyme(s) activating L-SD. The suggestion is made that production of a functional L-SD in vivo requires activation of the structural gene product by an enzyme or enzymes that reduce the protein to an active form.

Research paper thumbnail of L-serine degradation in Escherichia coli K-12: cloning and sequencing of the sdaA gene

Journal of bacteriology, 1989

A new mutant of Escherichia coli K-12 unable to grow with L-serine, glycine, and L-leucine has be... more A new mutant of Escherichia coli K-12 unable to grow with L-serine, glycine, and L-leucine has been isolated by lambda plac Mu insertion and shown to be deficient in L-serine deaminase activity. The corresponding gene, sdaA, has been cloned from a prototrophic strain, and the clone has been characterized and sequenced. The evidence is consistent with the hypothesis that sdaA is the structural gene for L-serine deaminase. However, other possibilities are also considered. No significant homology with previously reported DNA or protein sequences was detected.

Research paper thumbnail of The leucine regulon of Escherichia coli K-12: a mutation in rblA alters expression of L-leucine-dependent metabolic operons

Journal of bacteriology, 1990

We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the a... more We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the activity of a number of enzymes involved in different metabolic pathways, all of which are regulated by leucine. Selected for its ability to grow with L-serine as sole carbon source, the rbl-1::Tn10 mutant had high levels of L-serine deaminase activity (due to increased transcription of the structural gene) and of another amino acid-degrading enzyme, L-threonine dehydrogenase, and decreased transcription of the operons serA and ilvIH, coding for biosynthetic enzymes. The rbl mutation suppressed the slow growth of a metK mutant, deficient in S-adenosylmethionine synthetase. Furthermore, metK mutants spontaneously accumulated faster-growing rbl-like derivatives, and a commonly used metK strain, RG62, carries such a mutation. The rbl gene is located near 20 min on the E. coli genetic map. All phenotypes of the rbl mutant could be observed in rbl+ strains cultivated in the presence of L-leuci...

Research paper thumbnail of Derivation of glycine from threonine in Escherichia coli K-12 mutants

Journal of bacteriology, 1975

Escherichia coli AT2046 has been shown previously to lack the enzyme serine transhydroxymethylase... more Escherichia coli AT2046 has been shown previously to lack the enzyme serine transhydroxymethylase and to require exogenous glycine for growth as a consequence. Strains JEV73 and JEV73R, mutants derived from strain AT2046, are shown here to be serine transhydroxymethylase deficient, but able to derive their glycine from endogenously synthesized threonine. Leucine is shown to be closely involved in the regulation of biosynthesis of glycine, to spare glycine in strain AT2046T, to replace glycine in strain JEV73, and to increase threonine conversion to glycine in a representative prototroph of E. coli. An interpretation of strains JEV73 and JEV73R as regulatory mutants of strain AT2046 is given. A hypothesis as to the role of leucine as a signal for nitrogen scavenging is suggested.