Isolation and expression of the Rhodobacter sphaeroides gene (pgsA) encoding phosphatidylglycerophosphate synthase

The Rhodobacter sphaeroides pgsA gene (pgsA(Rs)), encoding phosphatidylglycerophosphate synthase (PgsA(Rs)), was cloned, sequenced, and expressed in both R. sphaeroides and Escherichia coli, As in E. coli, pgsA(Rs) is located immediately downstream of the uvrC gene, Comparison of the deduced amino acid sequences revealed 41% identity and 69% similarity to the pgsA gene of E. coli, with similar homology to the products of the putative pgsA genes of several other bacteria, Comparison of the amino acid sequences of a number of enzymes involved in CDP-diacylglgcerol-dependent phosphatidyltransfer identified a highly conserved region also found in PgsA(Rs). The pgsA(Rs) gene carried on multicopy plasmids was expressed in R. sphaeroides under the direction of its own promoter, the R. sphaeroides rrnB promoter, and the E. coli lac promoter, and this resulted in significant overproduction of PgsA(Rs) activity, Expression of PgsA(Rs) activity in E. coli occurred only with the E. coli lac promoter, PgsA(Rs) could functionally replace the E. coli enzyme in both a point mutant and a null mutant off. coli pgsA. Overexpression of PgsA(Rs) in either E. coli or R. sphaeroides did not have dramatic effects on the phospholipid composition of the cells, suggesting regulation of the activity of this enzyme in both organisms.