Overexpression of phosphatidylglycerophosphate synthase restores protein translocation in a secG deletion mutant of Escherichia coli at low temperature.

The E. coli secG deletion mutant is unable to grow and is defective in protein translocation at low temperature. A gene of Bacillus subtilis, which is able to restore the growth of the deletion mutant at low temperature, was found as a multi-copy suppressor. Sequencing of this gene revealed significant homology to E. coli pgsA, which encodes phosphatidylglycerophosphate synthase, an enzyme involved in acidic phospholipid synthesis. A plasmid carrying E. coli pgsA also restored the growth of the deletion mutant. Furthermore, protein translocation in the deletion mutant was stimulated when it harbored a plasmid carrying pgsA. A possible mechanism underlying the pgsA-dependent suppression of the secG deletion mutation is discussed.