Genetic studies on the β subunit of Escherichia coli RNA polymerase

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Abstract
A collection of 95 independent, spontaneously-occurring mutants carrying amber lesions that affect expression of the β gene, rpoB, has been isolated (see accompanying paper (Nene and Glass 1982)). Certain rpoB amber mutations act in trans, preventing a functional allele present on an F′ plasmid from acting at high temperature. Two such temperature-sensitive rpoB(Am) strains are shown to produce large, N-terminal amber fragments. The possibility that these truncated polypeptides are the cause of this trans-dominant conditional-lethal phenotype is supported by analysis of fragment levels in thermoresistant survivors: the nonsense fragments are degraded at a significantly faster rate (half-lives 1.4- to 2.6-fold reduced) in Ts+ derivatives likely to carry second-site mutations within rpoB. We suggest that the β fragments interfere with RNA polymerase function by interacting with one or more of the polymerase subunits.