Isolation of mutations in the α operon of Escherichia coli that suppress the transcriptional defect conferred by a mutation in the porin regulatory gene envZ

One class of mutations in the envZ gene of Escherichia coli K-12 confers a pleiotropic defect on the expression of several genes, including ompF, lamB, and phoA, that are otherwise not commonly regulated. Four second-site mutations that suppress this transcriptional defect have been isolated by using a procedure that circumvented the problem of intragenic suppressors, including true revertants. All four mutations have been mapped to the genes of the α operon and have been assigned tentatively to the gene rpoA, which specifies the α subunit of RNA polymerase. The mutations, referred to as sez (for suppressor of envZ), did not appear to confer a phenotype on an otherwise wild-type strain and did not suppress the transcriptional defects conferred by several other phenotypic classes of envZ mutations, including amber mutations. Our results led us to postulate that the α subunit or some other component of the α operon plays a role in determining the specificity of gene expression.