Effects of rifampicin resistant rpoB mutations on antitermination and interaction with nusA in Escherichia coli

Rifampicin resistant (Rifr mutations map in the rpoB gene encoding the beta subunit of Escherichia coli RNA polymerase. We have used our collection of 17 sequenced Rifr mutations to investigate the involvement of E. coli RNA polymerase in the antitermination systems enhancing expression of delayed early lambda genes or stable RNA. We have found that Rifr mutations affect both lambda N-mediated antitermination and the cellular antitermination system involved in synthesis of stable RNA. Because NusA is involved in antitermination and termination, we also investigated the interaction of NusA and RNA polymerase by determining whether Rifr mutations alter NusA-dependent termination or antitermination in cells with defective nusA alleles. We have shown that Rifr mutations can either enhance or suppress the phenotypes of defective nusA alleles. Most Rifr mutations alter the temperature range over which the nusA1 allele supports lambda N-mediated antitermination. In addition, a number of Rifr alleles restore termination to the nusA10(Cs) and the nusA11(Ts) mutants defective in this process. Our results indicate that the region of the rpoB gene defined by the Rifr mutations is involved in the antitermination process and affects the activity of the NusA protein directly or indirectly.     

An Escherichia coli mutant unable to support site-specific recombination of bacteriophage lambda

We report the isolation of mutations in, and the characterization of, an Escherichia coli gene, hip, that is required for site-specific recombination of phage lambda. hip mutants are recessive and are located near minute 20 on the linkage map. The gene product is not vital to bacterial growth, since deletion mutants are viable. The absence of hip product reduces lambda integration to barely detectable levels and also reduces prophage excision, but less drastically. Certain mutations in the lambda int gene partially restore integration and excision in hip- hosts. Homologous recombination promoted by recA does not require hip function. In addition to their defect in site-specific recombination, hip mutants are unable to support lytic growth of phage Mu or of certain lambda mutants. Their pleiotropic phenotype closely resembles that of himA mutants, but complementation, mapping and DNA sequencing show that hip and himA are different genes.