Genetic studies on the β subunit of Escherichia coli RNA polymerase

Abstract
The use of five different nonsense suppressors, in conjunction with a collection of 95 independent, spontaneously-occurring amber mutants affecting expression of rpoB, allows the generation of a maximum of 475 potential variants of the β subunit of E. coli RNA polymerase, each carrying a known amino acid substitution at a particular site. The effect of these amino acid exchanges has been investigated in vivo. A significant majority (363/475) of substitutions lead to cellular death and altered properties —temperature sensitivity, apparently altered transcription termination and a changed stringent response—indicating that RNA polymerase function (unlike that of dispensible proteins) is extremely sensitive to such single site changes.