Abstract
Abstract The DNA-dependent RNA polymerase (EC 2.7.7.6) of Azotobacter vinelandii has been obtained as a homogeneous protein of high and constant specific activity. At an ionic strength of 0.02 it exists as a species with s20,w0 = 22.9 S and a molecular weight of 782,000 daltons, but when the salt concentration is raised to 0.4 M it dissociates reversibly to a 14 S form with a reduction in molecular weight to half. The purification was dependent on the recognition of the existence of a 14 S species, presumably a degradation product of the polymerase, and its removal by fractionation. This 14 S material is stable in low salt buffers and has a low and variable polymerase activity. The stability and behavior of the 23 S species has been examined by analytical sedimentation under a variety of conditions of pH and ionic strength; after aging; and in the presence of sulfhydryl compounds, Mg2+, and other reagents. The amino acid composition and free sulfhydryl groups have been determined.
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