Role for fadR in unsaturated fatty acid biosynthesis in Escherichia coli.

Escherichia coli K-12 mutants constitutive for the synthesis of the enzymes of fatty acid degradation (fad) synthesize significantly less unsaturated fatty acid (UFA) than do wild-type (fadR+) strains. The constitutive fadR mutants synthesize less UFA than do fadR+) strains both in vivo and in vitro. The inability of fadR strains to synthesize UFAs at rates comparable to those of fadR+ strains is phenotypically asymptomatic unless the fadR strain also carries a lesion in fabA, the structural gene for beta-hydroxydecanoyl-thioester dehydrase. Unlike fadR+ fabA(Ts) mutants, fadR fabA(Ts) strains synthesize insufficient UFA to support their growth even at low temperatures and, therefore, must be supplemented with UFA at both low and high temperatures. The low levels of UFA in fadR strains are not due to the constitutive level of fatty acid-degrading enzymes in these strains. These results suggest that a functional fadR gene is required for the maximal expression of UFA biosynthesis in E. coli.