An Escherichia coli mutant defective in lipid export

Escherichia coli phospholipids and lipopolysaccharide, made on the inner su rface of the inner membrane, are rapidly transported to the outer membrane by mechanisms that are not well characterized. We now report a temperature- sensitive mutant (WD2) with an A270T substitution in a trans-membrane regio n of the ABC transporter MsbA. As shown by P-32(i) and C-14-acetate labelin g, export of all major lipids to the outer membrane is inhibited by similar to 90% in WD2 after 30 min at 44 degreesC, Transport of newly synthesized proteins is not impaired. Electron microscopy shows reduplicated inner memb ranes in WD2 at 44 degreesC, consistent with a key role for MsbA in lipid t rafficking.