Transcription in Yeast: Separation and Properties of Multiple RNA Polymerases

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RESUMO

Four peaks of DNA-directed RNA polymerase activity are resolved by salt gradient elution of a sonicated yeast cell extract on DEAE-Sephadex. The enzymes, which are named IA, IB, II, and III in order of elution, all appear to come from cell nuclei. Only enzyme II is sensitive to α-amanitin. All enzymes are more active with Mn++ than with Mg++ as divalent ion. Enzymes IB and II have salt optima in the range 0.05-0.10 M (NH4)2SO4, whereas enzyme III is maximally active at 0.20-0.25 M (NH4)2SO4. With optimal salt concentration and saturating DNA, the template preference ratio, activity on native calfthymus DNA divided by activity on denatured calf-thymus DNA, is 2.2 for IB, 0.4 for II, and 3.5 for III. None of the yeast polymerases was inhibited by rifamycin SV. Rifamycin AF/013 effectively inhibited polymerases IB, II, and III.

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