Long-chain fatty acid transport in Escherichia coli. Cloning, mapping, and expression of the fadL gene

Transport of long-chain fatty acids across the inner membrane of Escherichia coli K-12 requires a functional fadL gene (Maloy, S.R., Ginsburgh, C.L., Simons, R.W., and Nunn, W.D. (1981) J. Biol. Chem. 256, 3735-3742). Mutants defective in the fadL gene lack a 33,000-dalton inner membrane protein as evaluated using two-dimensional pI/sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (Ginsburgh, C.L., Black, P.N., and Nunn, W.D. (1984) J. Biol. Chem. 259, 8437-8443). In an effort to determine whether the fadL gene is the structural gene for this 33,000-dalton protein, we have cloned, mapped, and analyzed the expression of the fadL gene. The fadL gene has been localized on a 2.8-kilobase EcoRV fragment of E. coli genomic DNA. Plasmids containing this gene (i) complement all fadL mutants, (ii) increase the long-chain fatty acid transport activity of fadL strains harboring them by 2- to 3-fold, and (iii) direct the synthesis of a membrane protein which has the same molecular weight and isoelectric point as that described by Ginsburgh et al. This is a heat-modifiable protein which has an apparent molecular weight of 43,000 daltons when solubilized at 100°C in the presence of SDS and 33,000 daltons when solubilized at 50°C in the presence of SDS.