MOLECULAR ANALYSIS OF ASMA, A LOCUS IDENTIFIED AS THE SUPPRESSOR OF OMPF ASSEMBLY MUTANTS OF ESCHERICHIA-COLI K-12

We present the molecular characterization of the asmA gene, whose prod uct is involved in the assembly of outer membrane proteins in Escheric hia coli K-12. The asmA locus was initially identified as a site for s uppressor mutations of an assembly defective OmpF315. Our data suggest that these suppressor mutations either completely abolish or reduce a smA expression and can be complemented in trans by plasmid clones carr ying asmA sequences. The recessive nature of asmA suppressor mutations suggests that the functional AsmA protein participates in inhibiting the assembly of OmpF315 and other mutant OmpFs. As the assembly of wil d-type and parental OmpF proteins was not affected by asmA mutations, AsmA must provide an environment refractory only to the assembly of mu tant OmpF proteins. However, we cannot completely rule out the possibi lity that AsmA plays a minor role in the assembly of wild-type and par ental OmpF in wild-type cells. The presence of a putative signal seque nce within the amino-terminal sequence of AsmA suggests that it is eit her a periplasmic or an outer membrane protein. This predicted locatio n of AsmA is compatible with its role in the assembly of outer membran e proteins.