Nucleotide sequence of the petB gene encoding cytochrome b6 from the mesophilic cyanobacterium Synechocystis PCC...

The gene encoding the cytochrome b6 subunit (petB) of the cytochrome b6f complex has been isolated, cloned and sequenced by nonradioactive methods from genomic DNA of the unicellular cyanobacterium Synechocystis sp. PCC 6803. The coding region consists of 666 nucleotides, coding for a polypeptide with a molecular mass of 25.02 kDa. In contrast to higher plant petB sequences an aminoterminal extension of seven amino acids occurs. Aminoterminal sequencing of the isolated protein excludes--different from higher plants--the existence of an intron after the first amino acids but indicate the posttranslational removal of three amino acids from the amino terminus. The aminoterminal extension--found only in non-nitrogen-fixing, unicellular cyanobacteria--shows a high degree of homology between different species.