Robert Haselkorn - Academia.edu (original) (raw)

Papers by Robert Haselkorn

Photosynthesis Research, 2001

The genome of Rhodobacter capsulatus has been completely sequenced.

Nature, 1984

Biological nitrogen fixation requires the nitrogenase enzyme complex, ATP, and a strong reductant... more Biological nitrogen fixation requires the nitrogenase enzyme complex, ATP, and a strong reductant1. Klebsiella pneumoniae contains 15 linked nitrogen fixation (nif) genes2,3, three of which, nifH, nifD and nifK have been sufficiently conserved in evolution that cloned K. pneumoniae nifHDK DNA4 will hybridize to DNA sequences from every nitrogen-fixing bacterium examined to date, including the purple, non-sulphur bacterium Rhodopseudomonas capsulata5, in which one complete nifHDK operon has been mapped6. Using cloned K. pneumoniae nifHDK DNA we report here that R. capsulata contains multiple copies of the genes for nitrogenase components. Two regions containing sequences homologous to all three nif structural genes have been identified, and mutations in one region produced a Nif- phenotype. Nif+ pseudorevertants were derived from these mutants, some of which retained the original mutation suggesting that some of the extra nif gene sequences can be functionally activated.

Intervirology, 1983

ABSTRACT The Study Group finds it appropriate that viruses which have as their host cyanobacteria... more ABSTRACT The Study Group finds it appropriate that viruses which have as their host cyanobacteria (blue-gree algae) should be grouped within the well-categorized families of the bacterial viruses. Thus, the term cyanophage is adopted as a symptom for the vernacular name BGA virus (BGAV) originally given to this virus type.

Molecular Microbiology, 2010

Heterocysts are terminally differentiated cells that fix nitrogen in filaments of the cyanobacter... more Heterocysts are terminally differentiated cells that fix nitrogen in filaments of the cyanobacterium Anabaena PCC 7120. They differentiate from vegetative cells at regular intervals along each filament. The developmental process is initiated by an increase in the ratio of reduced carbon to reduced nitrogen. This cue triggers protein NtcA to activate transcription of nrrA, which leads to transcription of the hetR gene. HetR is a master transcription factor required for expression of many heterocyst-specific genes. One such gene is hetP, shown by Higa and Callahan in this edition of Molecular Microbiology to be able to replace hetR for most of the downstream events required for a functional heterocyst. Ectopic production of HetP in a hetR mutant allows the differentiation of heterocysts. These heterocysts can fix nitrogen under anaerobic conditions but they are unable to provide wild-type protection of nitrogenase from oxygen, so they cannot bypass all of the duties of HetR. Additionally, the 5Ј-flanking region of the hetP gene provides the best-characterized binding site for the HetR protein so far, a seven-base pair inverted repeat.

Current Biology, 2009

qy . The electron spin polarization ESP EPR signal arising from the P-700 A radical pair in Photo... more qy . The electron spin polarization ESP EPR signal arising from the P-700 A radical pair in Photosystem I PS I 1 . consisting of the oxidized PS I primary donor, P-700 , and the reduced vitamin K K acceptor, A , is studied as a 11 1 function of isotopic labelling of the native A acceptor. No pre-extraction of

… Nitrogen-fixing Bacteria and Cyanobacterial …, 2007

... The other potentially confounding factor in cyanobacterial genetics is the tremendous ploidy ... more ... The other potentially confounding factor in cyanobacterial genetics is the tremendous ploidy of the cells. ... differentiation more or less completely, such as hetR and hetN, whereas others that affected the pattern of differentiation were called pat, such as patA, patB and patS. ...

Molecular Microbiology, 2008

Although cytoplasmic bridges between adjacent cells in the filaments of nitrogen-fixing cyanobact... more Although cytoplasmic bridges between adjacent cells in the filaments of nitrogen-fixing cyanobacteria have been known for decades, the existence also of a continuous periplasm along the filaments raised the possibility that alternative modes of communication between cells could be utilized. The latter hypothesis was investigated by using GFP fusions to proteins whose expression is cell-specific and engineered to be transported into the periplasm. Two groups have recently obtained contradictory results, one supporting periplasmic transport of GFP from cell to cell, the other not. A third effort, involving members of the first group, used a smaller, soluble fluorophore and found rapid communication via the cytoplasmic bridges between cells. The dilemma of periplasmic diffusion remains unresolved.

Molecular and General Genetics, 1985

A library of Rhodopseudomonas capsulata chromosomal DNA was constructed in the broad host range c... more A library of Rhodopseudomonas capsulata chromosomal DNA was constructed in the broad host range cosmid vector pLAFR1. The library was used to isolate nitrogen fixation genes by complementation of R. capsulata Nif- mutants. Four complementing regions were localized on different cloned DNA fragments by Tn5 and mini-Mu mutagenesis. Additional nif genes were identified by recombination of transposons from the nif

Journal of Molecular Biology, 1966

The molecular weight of turnip yellow mosaic virus and its weight fraction of RNA were measured. ... more The molecular weight of turnip yellow mosaic virus and its weight fraction of RNA were measured. The mass of the virus was found to be 5·5 X 10 6 for the necrotic Rademacher strain and 5·7 X 10 6 for the savoy strain. The weight fraction of RNA was 0·35. These values are consistent with the model of the virus having only two species of macromolecules: the viral RNA and 180 identical polypeptide chains.

Proceedings of The National Academy of Sciences, 1995

A mutant strain of the cyanobacterium Synechocystis 6803, TolE4B, was constructed by genetic dele... more A mutant strain of the cyanobacterium Synechocystis 6803, TolE4B, was constructed by genetic deletion of the protein that links phycobilisomes to thylakoid membranes and of the CP43 and CP47 proteins of photosystem II (PSII), leaving the photosystem I (PSI) center as the sole chromophore in the photosynthetic membranes. Both intact membrane and detergent-isolated samples of PSI were characterized by time-resolved

The cyanobacterium Anabaena (Nostoc) PCC 7120 responds to starvation for nitrogen compounds by di... more The cyanobacterium Anabaena (Nostoc) PCC 7120 responds to starvation for nitrogen compounds by differentiating approximately every 10th cell in the filament into nitrogen-fixing cells called heterocysts. Heterocyst formation is subject to complex regulation, which involves an unusual response regulator PatA that contains a CheY-like phosphoacceptor (receiver, REC) domain at its C-terminus. PatA-like response regulators are widespread in cyanobacteria; one of

Plant Molecular Biology, 2002

We have applied a two-gene system based on the sequences of nuclear genes encoding multi-domain p... more We have applied a two-gene system based on the sequences of nuclear genes encoding multi-domain plastid acetyl-CoA carboxylase (ACCase) and plastid 3-phosphoglycerate kinase (PGK) to study grass evolution. Our analysis revealed that these genes are single-copy in most of the grass species studied, allowing the establishment of orthologous relationships between them. These relationships are consistent with the known facts of

Nature, 1996

Bacterium genome sequence. V Kumar, M Fonstein, R Haselkorn Nature 381:65846584, 653-654, 1996. S... more Bacterium genome sequence. V Kumar, M Fonstein, R Haselkorn Nature 381:65846584, 653-654, 1996. Stephen Oliver in his Progress article champions a systematic approach to the discovery of gene function so as to make ...

Molecular and General Genetics, 1989

We have determined the DNA sequence for the genes nifR1, nifR2 and nifR4 in the photosynthetic ba... more We have determined the DNA sequence for the genes nifR1, nifR2 and nifR4 in the photosynthetic bacterium Rhodobacter capsulatus. These genes regulate transcription of the nifHDK operon and so limit the expression of nitrogen fixation activity to periods of low environmental concentrations of both oxygen and fixed nitrogen. The sequences of these three genes are similar to components of the

Science, 1962

the scattered radiation from an oscillator, that it holds only for polarizations perpendicular to... more the scattered radiation from an oscillator, that it holds only for polarizations perpendicular to the direction of observation. The actual vanishing of the radiation for longitudinal polarization is not implied by the form given. The correct vector dependence on the polarization should be given, or the limitation duly noted.

A second nitrogen fixation (nif) operon in the cyanobacterium (blue-green alga) Anabaena (Nostoc)... more A second nitrogen fixation (nif) operon in the cyanobacterium (blue-green alga) Anabaena (Nostoc) sp. strain PCC 7120 has been identified and sequenced. It is located just upstream of the nifHDK operon and consists of four genes in the order nifB, fdxN, nifS, and nifU. The three nif genes were identified on the basis of their similarity with the corresponding genes from other diazotrophs. The fourth gene, fdxN, codes for a bacterial type ferredoxin (Mulligan, M. E., Buikema, W. J., and Haselkorn, R. (1988) J. Bacteriol. 167, 4406-4410). The four genes are probably transcribed as a single operon, but are expressed at a lower level than the nifHDK operon, and only after a developmentally induced DNA rearrangement occurs that excises a 55-kilobase pair element from within the fdxN gene (Golden, J. W., Mulligan, M. E., and Haselkorn, R. (1987) Nature 327, 526-529; Golden, J. W., Carrasco, C. D., Mulligan, M. E., Schneider, G. J., and Haselkorn, R. (1988) J. Bacteriol. 170, 5034-5041). The promoter for the nifB operon was located by primer extension. Comparison of the nifB 5'-flanking sequence with the nifH 5'-flanking sequence did not reveal any consensus base pairs that would define a nif promoter for Anabaena. The operon contains two instances of 7-base pair directly repeated sequences: seven copies of the repeated sequence are found between the nifB and fdxN genes and six copies are found between the nifS and nifU genes. The function of these repeats is unknown.

Plant Science - PLANT SCI, 2003

Switchgrass, Panicum virgatum, is a perennial grass native to the USA and Canada with an array of... more Switchgrass, Panicum virgatum, is a perennial grass native to the USA and Canada with an array of ploidy levels and ecotypes. In this study, genetic variation in the nuclear gene encoding plastid acetyl-CoA carboxylase from six switchgrass cultivars was investigated with the goal of defining relationships among these populations using DNA sequence comparisons. Four polymorphic sites were found in exons and 18 polymorphic sites plus four indels were found in introns within a 1828-nucleotide sequence alignment (696 nucleotides in exons and 1132 nucleotides in introns) of 27 genes. The homoeologous genomes of tetraploid and octaploid switchgrass are very closely related to each other, and among and between lowland and upland switchgrass ecotypes. Based on the molecular clock determined earlier for the Triticeae tribe, the genome divergence time and the time of the polyploidization events which established various contemporary switchgrass lineages was estimated to be less than 2 million...