Characterization of a ts β′ mutant RNA polymerase ofEscherichia coli

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Abstract
RNA polymerase isolated from ts XH56, a conditional lethal mutant unable to grow and synthesize RNA at 42°, was found to be temperature sensitive in vitro. The mutation affects the β′ subunit as determined by mixed reconstitution of isolated subunits from wild-type and mutant enzyme. The mutant RNA polymerase is unstable; addition of glycerol stabilizes the enzyme and increases its activity on native DNA. In addition, the mutant enzyme is sensitive to high ionic strength. Both high temperature and high ionic strength do not affect chain elongation; thus, the mutation renders the enzyme unable either to bind to or melt out promotor sites. From these data we conclude that the β′ subunit plays an important role in promotor selection.