Effect of Altered Lipid A Synthesis on the Synthesis of Major Proteins of the Salmonella typhimurium Outer Membrane

Abstract

The effect of altered lipid A synthesis on the synthesis of major outer membrane proteins was investigated in mutants of Salmonella typhimurium conditionally defective in the synthesis of 3-deoxy-d-mannooctulosonic acid (KDO). The defect is due to a mutation in the structural gene for KDO-8-phosphate synthetase (designated kdsA), and expression of this lesion results in the accumulation of a precursor of lipid A that not only lacks KDO but is also deficient in ester-linked fatty acyl residues. During the initial 20–30 min following a shift of mutants to nonpermissive conditions, the rate of synthesis of the OmpA protein increased ∼2.5-fold and then decreased. In contrast, the rates of synthesis of total cell-envelope proteins, as well as that of the porin proteins, were unaffected. The mechanism responsible for the initial increase in the rate of OmpA synthesis remains to be established. However, it appears that the subsequent decrease in the rate of OmpA synthesis may be related to a decrease in the stability of OmpA messenger RNA. The effect of non permissive conditions on the rate of OmpA synthesis was specifically related to expression of the kdsA lesion, and it was not found to be strain-specific or uniquely related to a single kdsA mutant allele.