Altered RNA Polymerases Resulting from Temperature-sensitive Mutations in the rif Region of the E. coli Chromosome

Abstract

INTRODUCTION
The isolation of mutants with altered RNA polymerases is important for the study of transcription and its control. Such mutations would not only shed light on the roles of the individual subunits (α, β, β′, σ) in the complex process of RNA synthesis, but might also provide information on the regulation of subunit synthesis itself. Strains carrying defective RNA polymerases can also be used to select unlinked suppressor mutations. These second-site mutations might reverse the effects of the original altered subunit through direct contact of a second altered subunit or factor which normally interacts with RNA polymerase. This approach may prove useful, therefore, for identifying additional subunit and factor genes. At present, the location of the structural genes for the β and β′ subunits is well established. These genes form a single operon transcribed in a clockwise fashion at approximately 79 minutes on the E. coli genetic map (Errington et al. 1974). Recently, the gene coding for the α subunit has been reported to be near the spc locus at 64 minutes (Jaskunas et al., this volume).

Mutations mapping at the rif locus (within the structural gene for the β subunit; Heil and Zillig 1970) result in strains resistant to the antibiotic rifampicin (Tocchini-Valentini, Marino and Colvill 1968), a specific inhibitor of RNA polymerase. We therefore attempted to isolate a large number of temperature-sensitive lethal mutations in the rif region of the chromosome, with the hope that some of these mutations would be in the structural genes for β...