SPECTRAL PROPERTIES OF CYANOBACTERIUM SYNECHOCYSTIS SP PCC-6803 MUTANTS LACKING PHOTOSYSTEM-II ACTIVITY

The photosynthetic apparatus of six previously obtained mutants of cya nobacterium Synechocystis sp. PCC 6803 devoid of photosystem II (PS II ) activity has been studied by fluorescence analysis and preparative e lectrophoresis. Mutations in the gene psbC eliminating or modifying mo re than 80% of the amino acid residues of CP43 were associated with th e absence of chlorophyll-containing PS II subunits in the membranes of strains SN5, SK15, and Delta 2. Chlorophyll-containing PS II subunits were detected in strains CP13 (a psbC mutant with a deletion of one a mino acid residue in CP43), PMB1 (a psbB mutant lacking four amino aci d residues in CP47) and SK4 (a psbB mutant with a truncated form of CP 47, lacking one third of the amino acid chain from the C-terminus of t he polypeptide). Judging by the fluorescence spectra at 77 K (F686) an d the position of the corresponding electrophoretic fractions in gels, the PS II subunits in CP13, PMB1, and SK4 formed only fragments of th e photosystem. It is concluded that fluorescence analysis and preparat ive electrophoresis can be used to detect mutant cyanobacteria capable of forming PS II fragments. Investigation of such mutants is useful f or understanding the mechanisms of PS II self-assembly.