Functional analysis of psbV and a novel c-type cytochrome gene psbV2 of the thermophilic cyanobacterium Thermosynechococcus elongatus strain BP-1

Cytochrome c-550 is an extrinsic protein associated with photosystem II (PS II) in cyanobacteria and lower eukaryotic algae and plays an important role in the water-splitting reaction. The gene (psbV) for cytochrome c-550 was cloned from the thermophilic cyanobacteria Thermosynechococcus (formerly Sy nechococcus) elongatus and T, (formerly Synechococcus) vulcanus, In both ge nomes, located downstream of psbV were a novel gene (designated psbV2) for a c-type cytochrome and petJ for cytochrome c-553. The deduced product of p sbV2 showed composite similarities to psbV and petJ, Phenotype of psbV-disr uptant in Thermosynechococcus was practically the same as that reported in Synechocystis sp, PCC 6803. Either psbV or psbV2 gene of T, elongatus was e xpressed in the psbV-disruptant of Synechocystis sp, PCC 6803, which result ed in recovery of the photoautotrophic growth. However, the enhanced requir ement of Ca2+ or Cl- ions in the psbV-disruptant of Synechocystis was suppr essed by expression of psbV but not by expression of psbV2, Thus, it is con cluded that psbV2 can partly replace the role of psbV in PSII, The close ta ndem arrangement of psbV/psbV2/petJ implies that psbV2 was created by gene duplication and intergenic recombination during evolution.