Isolation and characterization of chain-terminating nonsense mutations in a porin regulator gene, envZ.

We isolated four independent amber mutations in gene envZ, whose product is involved in the regulation of porin protein genes ompF and ompC. The envZ amber strains exhibit an OmpF-/+ OmpC- porin phenotype and express other envelope protein genes at wild-type levels. This phenotype is clearly different from that of the previously isolated class of envZ mutants that exhibit an OmpF- OmpC+ phenotype and a pleiotropic decrease in the expression of several exported protein genes, including lamB and phoA. The addition of the local anesthetic procaine to wild-type strains also causes a pleiotropic decrease in the expression of genes ompF, lamB, and phoA. However, procaine has no effect on the synthesis of LamB or PhoA protein in the envZ amber strains. Thus, although EnvZ protein is required for the full expression of ompF and ompC, it apparently is not normally involved in the expression of other envelope protein genes. One interpretation of these results is that the EnvZ protein can be altered either by mutation or by procaine to a form that interferes with the expression of several envelope protein genes other than ompF and ompC. Finally, complementation analysis with ompR insertion mutations supports the physical data of Mizuno et al. (J. Biol. Chem 257:13692-13698, 1982) that suggest that envZ is cotranscribed with ompR from a single promoter in the order ompR envZ.