Mitochondria circular RN As are absent in sporulating cells of Saccharomyces cerevisiae (original) (raw)
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Archives of Biochemistry and Biophysics, 1971
A study of yeast mitochondrial RNA showed that although this RNA sediments in sucrose density gradients considerably slower than cytoplasmic ribosomal RNA, both RNA species have very similar electrophoret,ic mobilit,ies on polyacrylamide gels. Denaturation in formaldehyde results in a relat,ively larger decrease in the rate of sedimentation of mitochondrial RNA than of cytoplasmic ribosomal RNA or Escherichia coli ribosomal RNA. This suggests that hydrogen bonding is relatively more important as a stabilizing factor of the secondary structure of mitochondrial ribosomal RNA than of the latter two RNA species. This result also demonstrates that profound differences exist between mitochondrial ribosomal RNA and bacterial ribosomal RNA. Cycloheximide, a powerful inhibitor of the formation of cytoplaamic ribosomal RNA, was also found to inhibit the formation of the mitochondrial225 and 155 RNA components. This shows that the formation of t,hese RNA species is controlled by cytoplasmic protein formation. Fractionation of yeast mitochondrial RNA by sucrose density gradient centrifugation followed by hybridization of the individual fractiorls with mitochondrial and nuclear DNA showed that a considerable degree of homology exists between mitochondrial DNA and a mitochondrial RNA fraction sedimenting at about 19s. This is most likely metabolically stable messenger RNA, and it cannot, be concluded from hybridization experiments between total mitochondrial RNA and mitochondrial DNA that mitochondrial ribosomal RNA is transcribed from mitochondrial DNA. Mitochondrial RNA homologous to nuclear DNA was found to sediment as materia.1 closely similar to the 225 component. The usefulness of sodium iodide gradiel1t.s for the fractionation of total yeast DNA into its mitochondrial and nuclear components is described.
Messenger ribonucleic acid and protein metabolism during sporulation of Saccharomyces cerevisiae
Journal of Bacteriology
To investigate differences between growing yeasts and those undergoing sporulation, we compared several parameters of messenger ribonucleic acid (RNA) transcription and translation. The general properties of messenger RNA metabolism were not significantly altered by the starvation conditions accompanying sporulation. The average messenger RNA half-life, calculated from the kinetics of incorporation of [3H]adenine into polyadenylic acid-containing RNA, was 20 min in both cell populations. Furthermore, 1.3 to 1.4% of the total RNA was adenylated in both growing and sporulating cells. However, the proportion of RNA that could be translated in a wheat germ system slowly decreased during sporulation. Within 8 h after the induction of sporulation, isolated RNA stimulated half as much protein synthesis as the equivalent amount of vegetative RNA. There were significant differences in protein synthesis. The percentage of ribosomes in polysomes decreased threefold as the cells entered sporulation. This decrease began within 5 min of the initiation of sporulation, and the steady-state pattem was attained within 120 min. However, the ribosomes were not irreversibly inactivated; they could be reincorporated into polysomes by returning the sporulating cells to growth medium. Though unable to sporulate, strains homozygous for mating type, MATa/MATa, showed a similar decrease in the number of polysomes when placed in sporulation medium. Furthermore, the same shift toward monosomes was observed during stationary phase of growth. We conclude that the redistribution of ribosomes represents a general metabolic response to starvation. Our data indicate that the loss of polysomes is most likely caused by a decrease in the initiation of translation rather than a severe limitation in the amount of messenger RNA. Furthermore, the loss of polysomes is not due to the decreased synthesis of a major class of abundant proteins. Of the 400 vegetative proteins resolved by two-dimensional gel electrophoresis, only 19 were not synthesized by sporulating cells. Approximately 10 to 20% of the cells in a sporulating culture failed to complete ascus fornation. We have shown that [3S]methionine is incorporated equivalently into cells committed to sporulation and cells that fail to form asci. Furthermore, the proteins synthesized by these two populations were indistinguishable on one-dimensional gels. We compared proteins labeled by various protocols, including long-term and pulse-labeling during sporulation and prelabeling during vegetative growth before transfer to sporulation medium. The resulting two-dimensional gel patterns differed significantly. Many spots labeled by the long-term techniques may have arisen by protein processing. We suggest that pulse-labeling produces the most accurate reflection of instantaneous synthesis of proteins.
MGG Molecular & General Genetics, 1975
Yeast cells grown anaerobically have been shown to vary in their ultrastructure and absorption spectrum depending upon the composition of the growth medium. The changes observed in the anaerobically grown cells are governed by the availability of unsaturated fatty acids and ergosterol and a catabolite or glucose repression. All the cells contain nuclear and plasma membranes, but the extent of the occurrence of vacuolar and mitochondrial membranes varies greatly with the growth conditions. Cells grown anaerobically on the least nutritive medium, composed of 0.5% Difco yeast extract-5 % glucose-inorganic salts (YE-G), appear to contain little vacuolar membrane and no clearly recognizable mitochondrial profiles. Cells grown anaerobically on the YE-G medium supplemented with Tween 80 and ergosterol contain clearly recognizable vacuolar membrane and some mitochondrial profiles, albeit rather poorly defined. Cells grown on YE-G medium supplemented only with Tween 80 are characterized by the presence of large amounts of cytoplasmic membrane in addition to vacuolar membrane and perhaps some primitive mitochondrial profiles. When galactose replaces glucose as the major carbon source in the medium, the mitochondrial profiles within the cytoplasm become more clearly recognizable and their number increases. In aerobically grown cells, the catabolite repression also operates to reduce the total number of mitochondrial profiles. The possibility is discussed that cells grown anaerobically on the YE-G medium may not contain mitochondrial membrane and, therefore, that such cells, on aeration, form mitochondrial membrane from nonmitochondrial sources. A wide variety of absorption compounds is observed in anaerobically grown cells which do not correspond to any of the classical aerobic yeast cytochromes. The number and relative proportions of these anaerobic compounds depend upon the composition of the growth medium, the most complex spectrum being found in cells grown in the absence of lipid supplements.
Current Genetics, 2000
We elaborated a simple method that allows the transfer of mitochondria from collection yeasts to Saccharomyces cerevisiae. Protoplasts prepared from dierent yeasts were fused to the protoplasts of the ade2-1, ura3-52, kar1-1, q 0 strain of S. cerevisiae and were selected for respiring cybrids on plates containing 5uoroorotic acid and a non-fermentable carbon source. The identity of putative cybrids was assessed by restriction analysis of mitochondrial DNA, pulse ®eld electrophoresis and tetrad analysis. In the comprehensive screening, only mitochondrial genomes from synonymous species (S. italicus, S. oviformis, S. capensis and S. chevalieri) exhibited complete compatibility with S. cerevisiae nuclei. The closely related S. douglasii mitochondrial genome could also partially restore respiration-de®ciency in q 0 S. cerevisiae, whereas mitochondrial genomes from phylogenetically less related species could not.
Philosophical Transactions of the Royal Society B: Biological Sciences, 1988
We describe several yeast nuclear mutations that specifically block expression of the mitochondrial genes encoding cytochrome c oxidase subunits II (COXII) and III (COXIII). These recessive mutations define positive regulators of mitochondrial gene expression that act at the level of translation. Mutations in the nuclear gene PET111 completely block accumulation of COXII, but the COXII mRNA is present in mutant cells at a level approximately one-third of that of the wild type. Mitochondrial suppressors of pet 111 mutations correspond to deletions in mtDNA that result in fusions between the cox II structural gene and other mitochondrial genes. The chimeric mRNAs encoded by these fusions are translated in pet 111 mutants; this translation leads to accumulation of functional COXII. The PET111 protein probably acts directly on cox II translation, because it is located in mitochondria. Translation of the mitochondrially coded mRNA for COXIII requires the action of at least three nuclear ...
Journal of Bacteriology, 1967
Crosses were made between haploid wild-type and suppressive petite strains of bakers' yeast to obtain zygotes for analysis of mitochondrial heterogeneity. Wild-type × petite zygotes contained about 40% noncristate mitochondria when immediate mating mixtures were examined. The frequency of defective mitochondria had decreased to an average of 9.2% in 1-week-old zygote isolate cultures, and to 4.4% in slant cultures 1.5 years after initial zygote isolation. The latter value was not significantly different from values obtained with wild × wild zygotes of either age. The noncristate mitochondria were of two types: one lacking inner membrane invaginations or elaborations and the other containing concentrically arranged loops of inner membrane. The significance of these two types of respiration-deficient mitochondria is unknown. The gradual decrease in frequency of noncristate mitochondria, perhaps due to selection pressures in mixed chondriomes, was discussed as a further indication ...