A NEW-TYPE OF CYTOCHROME-C FROM SYNECHOCYSTIS PCC6803

A gene encoding a c-type cytochrome, designated cytM, was discovered 3.4 kbp downstream from the desA gene in the genome of Synechocystis PCC6803. The amino acid sequence derived from the nucleotide sequence exhibits about 35% similarity to the amino acid sequences of cytochromes c-553 from other cyanobacteria and eukaryotic algae, but it also includes regions typical of soluble c-type cytochromes from eukaryotic mitochondria. The molecular mass of the putative mature protein was estimated to be 8.3 kDa, and the isoelectric point was calculated to be 7.3. The amino-terminal region of the putative product of the cytM gene is hydrophobic, suggesting that this domain may be a transit peptide or a membrane anchor. Both photosynthesis and respiration in a mutant with a disrupted cytM gene were as efficient as they were in the wild-type strain.