THE SECG DELETION MUTATION OF ESCHERICHIA-COLI IS SUPPRESSED BY EXPRESSION OF A NOVEL REGULATORY GENE OF BACILLUS-SUBTILIS

SecG, a membrane component of E. coli protein translocase, stimulates the translocation of proteins across the cell membrane through the cyc le of topology inversion, which is coupled to the membrane-insertion a nd deinsertion cycle of SecA [Nishiyama et al, (1996) Cell 85, 71-81], A gene of B. subtilis able to suppress the cold-sensitive phenotype o f the secG deletion mutant of E. coli was cloned and found to encode a novel regulatory protein, ScgR, Similarity search revealed homology w ith known proteins such as GlnR of B. subtilis. Plasmid-encoded ScgR s timulated protein translocation in the deletion mutant. ScgR increased the proportion of cardiolipin at the expense of phosphatidylglycerol, but did not affect the composition of other lipid components of the c ell, suggesting that the increased cardiolipin level compensates for t he SecG function and thereby stimulates protein translocation.