Anabaena 7120 is a filamentous cyanobacterium that fixes nitrogen in heterocysts, specialized cells that develop at intervals along the filament in response to combined nitrogen deprivation. This study began as an investigation of nifH*, a gene 83% identical to the sequence encoding nitrogenase reductase, part of the nitrogen fixation complex. Although mutational analysis was not successful, transcriptional analysis demonstrated that nifH* is not expressed along with nifH in heterocysts of filaments deprived of combined nitrogen under aerobic conditions. Rather, expression of nifH* was detected only during anaerobic induction, at which time nifH is also highly expressed. Sequencing of the region adjacent to nifH* revealed four open reading frames. One of these was identified in a database search by homology to other sequences and encodes an enzyme which appears to act in the catabolism of endogenous glycogen reserves. The cyanobacterial gene is transcribed in exponentially growing cultures but not during anaerobic induction in which metabolic processes have been severely curtailed. There is no evidence that the gene is specifically involved in nitrogen fixation although it is expressed in heterocysts. The other three open reading frames were not identifiable by database comparison. ORF2 is expressed at low levels under the same condition as nifH* (anaerobic induction). ORF3 is probably expressed at very low levels under the same conditions as nifH (nitrogen deficiency and anaerobic induction) and the transcript may be large enough to include unsequenced regions upstream. Transcription of ORF4 was not detected under the conditions investigated.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8518 |
| Date | 01 January 1992 |
| Creators | Cannell, Barbara Ann |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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