Photosystem II genes isiA, psbDI and psbC in Anabaena sp. PCC 7120: cloning, sequencing and the transcriptional regulation in iron-stressed and iron-repleted cells.
Under conditions of iron deprivation cyanobacteria produce flavodoxin to replace ferredoxin as the terminal electron acceptor of photosynthesis. In unicellular cyanobacteria, the gene for flavodoxin is the second open reading frame in a dicistronic operon whose transcription is tightly regulated by iron. The first gene, isiA, produces a protein that is very similar to CP43, a chlorophyll-binding, antenna protein of the photosystem II reaction center. In the filamentous, heterocystous cyanobacterium Anabaena sp. PCC 7120, isiA and the gene for flavodoxin are located in separate operons with independent promoters. In this paper, we report on the sequence of isiA and show that it is found in a monocistronic operon that is transcriptionally regulated to be expressed under iron stress but does not produce detectable transcripts under conditions of iron repletion. We also report on the sequence, organization and expression of the gene that codes for CP43, psbC. In Anabaena sp. PCC 7120, psbC has a genetic organization similar to that of other cyanobacteria and higher plants; the 5' end of psbC overlaps the 3' end of psbDI. Transcriptional analysis of the psbDC operon showed that it is constitutively expressed in both iron-repleted and iron-stressed conditions; however, a new monocistronic transcript was detected that contains psbC and is preferentially expressed under iron stress conditions.
Leonhardt
K
K
Department of Botany, University of Toronto, Ontario, Canada.
Straus
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NA
D000595:Amino Acid Sequence; D017033:Anabaena / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics; D003001:Cloning, Molecular; D004247:DNA; D017931:DNA Primers; D005786:Gene Expression Regulation; D007501:Iron / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics*; D045332:Photosystem II Protein Complex; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C083100:photosystem II, chlorophyll binding protein, CP-43; C085993:psbDI protein, cyanobacteria; C076726:chlorophyll A binding protein CP43, Cyanobacteria; D004247:DNA; D007501:Iron