Am. Roy et J. Coleman, MUTATIONS IN FIRA, ENCODING THE 2ND ACYLTRANSFERASE IN LIPOPOLYSACCHARIDE BIOSYNTHESIS, AFFECT MULTIPLE STEPS IN LIPOPOLYSACCHARIDE BIOSYNTHESIS, Journal of bacteriology, 176(6), 1994, pp. 1639-1646
The product of the firA (ssc) gene is essential for growth and for the
integrity of the outer membrane of Escherichia coli and Salmonella ty
phimurium. Recently, Kelly and coworkers (T. M. Kelly, S. A. Stachula,
C. R. H. Raetz, and M. S. Anderson, J. Biol. Chem., 268:19866-19874,
1993) identified firA as the gene encoding UDP-3-O-(R-3-hydroxymyristo
yl)-glucosamine N-acyltransferase, the third step in lipid A biosynthe
sis. We studied the effects of six different mutations in firA on lipo
polysaccharide synthesis. All of the firA mutants of both E. coli and
S. typhimurium examined had a decreased lipopolysaccharide synthesis r
ate. E. coli and S. typhimurium strains defective in firA produced a l
ipid A that contains a seventh fatty acid, a hexadecanoic acid, when g
rown at the nonpermissive temperature. Analysis of the enzymatic activ
ity of other enzymes involved in lipid A biosynthesis revealed that th
e firA mutations pleiotropically affect lipopolysaccharide biosynthesi
s. In addition to that of UDP-3-O-(R-3-hydroxymyristoyl)-glucosamine N
-acyltransferase, the enzymatic activity of the lipid A 4' kinase (the
sixth step of lipid A biosynthesis) was decreased in strains with eac
h of the firA mutations examined. However, overproduction of FirA was
not accompanied by overexpression of the lipid A 4' kinase.