EXAMINATION OF ASMA AND ITS EFFECT ON THE ASSEMBLY OF ESCHERICHIA-COLI OUTER-MEMBRANE PROTEINS

asmA mutations were isolated as extragenic suppressors of an OmpF asse mbly mutant, OmpF315. This suppressor locus produced a protein that wa s present in extremely low levels and could only be visualized by West ern blotting in cells where AsmA expression was induced from a plasmid . Detailed fractionation analyses showed that AsmA localized with the inner membrane. Curiously, however, the mutant OmpF assembly step infl uenced by AsmA occurred in the outer membrane, perhaps indicating an i ndirect involvement of AsmA in the assembly of outer membrane proteins . Biochemical examination of the outer membrane showed that asmA null mutations reduce lipopolysaccharide (LPS) levels, thereby lowering the ratios of glycerolphospholipids to LPS and envelope proteins to LPS i n the outer membrane. Despite these quantitative alterations, no appar ent structural changes in LPS or major phospholipids were noted. Reduc ed LPS levels in asmA mutants indicate a possible role of AsmA in LPS biogenesis. Data presented in this study suggest that asmA-mediated Om pF assembly suppression may have been achieved by altering the outer m embrane fluidity, thus making it more amenable for the assembly of mut ant proteins.