CONTROL BY PHOSPHATIDYLGLYCEROL OF EXPRESSION OF THE FLHD GENE IN ESCHERICHIA-COLI

We reported elsewhere that mutation in the pgsA gene, responsible for the synthesis of phosphatidylglycerol, repressed the synthesis of flag ellin and caused the loss of motility of Escherichia coli (Tomura et a l., FEES Letters 329, 287-290, 1993). We now describe evidence for a d ecrease in promoter activity of the flhD gene, a master gene for flage llum synthesis, in the pgsA3 mutant. We constructed a plasmid with a p romoter region of the flhD gene connected with the structure region of the lacZ gene. The activity of beta-galactosidase in the extract prep ared from the pgsA3 mutant harboring the fusion plasmid was 30% of tha t in the wild type cells. This result means that phosphatidylglycerol is likely to be required for the initiation of transcription of the fl hD gene. We also found that the motility-less phenotype of the mutant was partially suppressed by elevating incubation temperature. This sup pression is caused by restoration of transcription of the flhD gene by high temperature. As the content of phosphatidylglycerol did not incr ease by elevating incubation temperature, we proposed that this suppre ssion is caused by alternation of a physical structure of phospholipid bilayers in cytoplasmic membranes.