CLONING AND CHARACTERIZATION OF THE PSAE GENE OF THE CYANOBACTERIUM SYNECHOCOCCUS SP PCC 7002 - CHARACTERIZATION OF A PSAE MUTANT AND OVERPRODUCTION OF THE PROTEIN IN ESCHERICHIA-COLI

The psaE gene, encoding a 7.5 kDa peripheral protein of the photosyste m I complex, has been cloned and characterized from the cyanobacterium Synechococcus sp. PCC 7002. The gene is transcribed as an abundant mo nocistronic transcript of approximately 325 nt. The PsaE protein has b een overproduced in Escherichia coli, purified to homogeneity, and use d to raise polyclonal antibodies. Mutant strains, in which the psaE ge ne was insertionally inactivated by interposon mutagenesis, were const ructed and characterized. Although the PS I complexes of these strains were similar to those of the wild type, the strains grew more slowly under conditions which favour cyclic electron transport and could not grow at all under photoheterotrophic conditions. The results suggest t hat PsaE plays a role in cyclic electron transport in cyanobacteria.