AN ESCHERICHIA-COLI GENE (FABZ) ENCODING (3R)-HYDROXYMYRISTOYL ACYL CARRIER PROTEIN DEHYDRASE - RELATION TO FABA AND SUPPRESSION OF MUTATIONS IN LIPID A BIOSYNTHESIS

Escherichia coli strain SM101 harbors a temperature-sensitive allele ( lpxA2) of the gene encoding UDP-GlcNAc acyltransferase (the first enzy me of the lipid A pathway), SM101 is temperature-sensitive for lipid A biosynthesis and growth, To determine whether or not E. coli mutants lacking lipid A can be isolated, we examined temperature-resistant rev ertants of SM101, All regained the ability to synthesize lipid A. Howe ver, some were not true revertants but had acquired mutations in a nei ghboring gene (orf17), while retaining the original lpxA2 lesion, Cell extracts of such revertants displayed 2-5 fold reductions in the spec ific activity of (3R)-hydroxymyristoyl-ACP dehydrase, Wild-type cells that overproduced the protein encoded by orf17 overproduced (3R)-hydro xymyristoyl-ACP dehydrase activity as much as 170-fold, suggesting tha t orf17 is the structural gene for the dehydrase. The proposed functio n of orf17 is further supported by its sequence similarity to fabA, th e structural gene for (3R)-hydroxydecanoyl dehydrase of E. coli. We su ggest that bypass of the lpxA2 phenotype by mutations in orf17 may be due to an increased (3R)-hydroxymyristoyl-ACP pool. The orf17 gene (wh ich we now designate fabZ) is not regulated by fadR, However, orf17 ma y be related to sefA, a suppressor of certain lesions in the cell divi sion/lipid A biosynthesis gene, envA.