GENE STPA INVOLVED IN THE ESTABLISHMENT OF SALT TOLERANCE IN THE CYANOBACTERIUM SYNECHOCYSTIS PCC6803

Na(s)431, a mutant of the cyanobacterium Synechocystis PCC6803, was is olated for its inability to grow on more than 0.1 M NaCl, as compared to 0.85 M for the wild-type. The gene, responsible for the salt sensit ivity phenotype, was cloned by complementation. This locus, stpA (salt -tolerant protein A), coded for a 45 kD protein. Comparative analysis of Na(s)431 and stpA :: Km(r) clone pointed to the presence of two mut ations in Na(s)431 and to the pleiotropic phenotype associated to a st pA- allele, i.e., sensitivity to several ions and impairment of the ca pacity to increase the amount of osmoprotectants and the activities of the thylakoid-located cytochrome c oxidase and Photosystem I cyclic e lectron transfer, as occurring in the wild type, when subjected to sal t stress. The possible role of the StpA protein in the establishment o f salt tolerance is discussed.