9.B.121 The AsmA (AsmA) Family
AsmA mutations were isolated as extragenic suppressors of an OmpF assembly mutant, OmpF315 in E. coli (Deng and Misra, 1996). This suppressor locus encoded a protein that was present in low levels and could only be visualized by Western blotting in cells where AsmA was overproduced. AsmA localized with the inner membrane, but the mutant OmpF assembly step influenced by AsmA occurred in the outer membrane. AsmA null mutations reduced lipopolysaccharide (LPS) levels, thereby lowering the ratios of glycerolphospholipids to LPS and envelope proteins to LPS in the outer membrane. Despite these quantitative alterations, no apparent structural changes in LPS or major phospholipids were noted. Reduced LPS levels in asmA mutants indicated a possible role of AsmA in LPS biogenesis (Deng and Misra, 1996).