CLONING AND NUCLEOTIDE-SEQUENCE OF REGA, A PUTATIVE RESPONSE REGULATOR GENE OF RHODOBACTER-SPHAEROIDES

A 0.9 kb DNA fragment carrying the Rhodobacter capsulatus regA gene, w hich encodes an oxygen-dependent, positively-acting response regulator of photosynthetic gene expression, was used as a probe in Southern hy bridisation experiments to determine whether a similar gene occurs in R. sphaeroides. A strongly hybridising DNA fragment isolated from a R. sphaeroides plasmid gene bank was isolated, sequenced and found to co ntain an open reading frame which exhibits 75% identity with the R. ca psulatus regA gene. The deduced amino acid sequence of 184 residues sh ows 81% identity and 89% similarity with the R. capsulatus RegA protei n, and significant similarities with other response regulators of the two component sensor-regulator type. Introduction of the R. sphaeroide s gene into a R. capsulatus regA mutant, which exhibits abnormally low levels of membrane-bound photosynthetic complexes, resulted in a 22-3 3-fold increase in these complexes to approximately 62-65% of wild-typ e levels. This is the first study to identify a putative response regu lator in R. sphaeroides and to complement a regulatory mutation in R. capsulatus with a gene from another species. Further studies of associ ated genes may identify the different mechanisms by which the regulati on of photosynthesis complex formation occurs in response to environme ntal stimuli in R. sphaeroides and R. capsulatus.