CLONING AND SEQUENCING OF MUTANT PSBB GENES OF THE CYANOBACTERIUM SYNECHOCYSTIS PCC-6803

Ten strains from a collection of mutants of Synechocystis 6803 defective in Photosystem II (PS II) function were transformed with chromosomal DNA of wild-type and mutant cells. Cross hybridization data allowed to identify four groups of PS II-mutants. Highly efficient transformation was observed between different mutant groups, but not within the groups. Restoration of photosynthetic activity of the mutant cells was also achieved by transformation with different parts of a 5.6 kb BamHI fragment of wild type Synechocystis DNA containing the psbB gene. Each group of mutants was transformed to photoautotrophic growth by specific subfragments of the psbB gene. DNA fragments of four selected mutant strains hybridizing with the psbB gene were isolated and sequenced. The mutations were identified as a single nucleotide insertion or substitution leading to stop codon formation in two of the mutants, as a deletion of 12 nucleotides, or as a nucleotide substitution resulting in an amino acid substitution in the other two mutants. Deletion of 12 nucleotides in mutant strain PMB1 and stop codon formation in strain NF16 affect membrane-spanning regions of the gene product, the CP 47 protein.