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R Haselkorn

Publications and source records attributed to R Haselkorn.

167 records · Page 10Linked to original sources
PubMedDate not supplied

Organization and transcription of genes important in Anabaena heterocyst differentiation.

The structural genes for nitrogenase and nitrogenase reductase have been cloned from Anabaena and physically mapped. The map differs from that of Klebsiella in several ways, including the insertion of 11 kbp between nifK and nifD in Anabaena. One nif RNA transcript has been studied in detail and shown to originate from a site in the Anabaena chromosome which lacks good correspondence with a typical prokaryotic strong promoter, suggesting the possibility of a need for positive activation. The nifH message is unstable or repressed or both under aerobic conditions. This feature is sufficient to account for the need for heterocyst differentiation in order for Anabaena to fix nitrogen aerobically. Structural genes for glutamine synthetase and the large subunit of RuBP carboxylase were also cloned, mapped and used to study transcription. In each case, the level of messenger RNA following nitrogenase induction is consistent with regulation of these genes at the level of transcription.

Chromosome Mapping↗
PubMedDate not supplied

Activation of extra copies of genes coding for nitrogenase in Rhodopseudomonas capsulata.

Biological nitrogen fixation requires the nitrogenase enzyme complex, ATP, and a strong reductant. Klebsiella pneumoniae contains 15 linked nitrogen fixation (nif) genes, three of which, nifH, nifD and nifK have been sufficiently conserved in evolution that cloned K. pneumoniae nifHDK DNA will hybridize to DNA sequences from every nitrogen-fixing bacterium examined to date, including the purple, non-sulphur bacterium Rhodopseudomonas capsulata, in which one complete nifHDK operon has been mapped. 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.

Chromosome Deletion↗
PubMedDate not supplied

Rearrangement of nitrogen fixation genes during heterocyst differentiation in the cyanobacterium Anabaena.

Nitrogen fixation by the cyanobacterium Anabaena is carried out in heterocysts, specialized, non-dividing cells which differentiate under conditions of ammonia or nitrate deprivation. In Anabaena, heterocyst differentiation is accompanied by rearrangement of some nitrogen fixation genes. A site-specific recombination between an 11 base-pair direct repeat sequence flanking the nifK and nifD genes removes 11 kilobases of intervening DNA, resulting in juxtaposition of the two genes and an alteration of the nifD protein-coding sequence.

Cell Differentiation↗
PubMedDate not supplied

Different recombination site specificity of two developmentally regulated genome rearrangements.

In the absence of a combined nitrogen source, such as ammonia, approximately every tenth vegetative cell along filaments of the cyanobacterium Anabaena develops into a heterocyst, a terminally differentiated cell that is morphologically and biochemically specialized for nitrogen fixation. At least two specific DNA rearrangements involving the nitrogen-fixation (nif) genes occur during heterocyst differentiation, one within the nifD gene and the other near the nifS gene. The two rearrangements have several properties in common. Both occur quantitatively in all heterocyst genomes, both occur at approximately the same developmental time, late in the process of heterocyst differentiation, and both result from site-specific recombination between short repeated DNA sequences. We report here the nucleotide sequences found at the site of recombination near the nifS gene. These sequences differ from those found previously for the nifD rearrangement, suggesting that the two rearrangements are catalysed by different enzymes and may be regulated independently. We also show that the nifS gene is transcribed only from rearranged genomes.

Cyanobacteria↗