Regulation of fatty acid transport in Escherichia coli: analysis by operon fusion.

The regulation of the fadL gene, which encodes a long-chain fatty acid (LCFA) transport component, was examined by constructing a strain of Escherichia coli K-12 that bears a phi (fadL-lacZ+) operon fusion plus a wild-type fadL gene. This merodiploid strain expressed LCFA transport and beta-galactosidase activity coordinately under noninducing, inducing, and catabolite-repressing conditions. Merodiploid strains which carried a defective fadR gene expressed LCFA transport and beta-galactosidase activity constitutively. These results suggest that expression of the fadL gene is regulated by the fadR gene and is inducible at the level of transcription by LCFA.