Transport of long chain fatty acids in Escherichia coli. Identification of a membrane protein associated with the fadL gene.

The fadL gene is required for the transport of long chain fatty acids in Escherichia coli (Maloy, S. R., Ginsburgh, C. L., Simons, R. W., and Nunn, W. D. (1981) J. Biol Chem. 256, 3735-3742). In an effort to define the fadL gene product(s), the membrane proteins of 16 independently isolated fadL mutants and wild type strains were compared by two-dimensional gel electrophoretic analysis. These studies indicated that (i) whenever a fadL mutation was present, a 33,000-dalton inner membrane protein was consistently absent, (ii) genetic restoration of mutant alleles to fadL+ resulted in the reappearance of this 33-kDa protein, and (iii) a reversion event mapping to the fadL gene produced a 33-kDa protein with altered electrophoretic properties. Mutations in the other known fad structural genes do not affect 33-kDa protein synthesis and the expression of the 33-kDa protein is physiologically regulated in a manner similar to the known fad enzymes. Overall, these studies suggest there is a close relationship between the 33-kDa inner membrane protein and the fadL gene which putatively codes for a fatty acid transport component(s).