Characterization of three subclasses of DNA-dependent RNA polymerases C from calf thymus.

DNA-dependent RNA polymerases from calf thymus tissue were solubilized and purified. Among seven chromatographically different forms of RNa polymerases obtained on DEAE-cellulose or DEAE-Sephadex chromatographies three subclasses of enzymes C were found. General enzymatic properties as: a moderate sensitivity to alpha-amanitin, divalent cation requirements, the preference for native DNA, efficient transcription of poly[d(A-T)], were similar to those described for C RNA polymerases from other sources. The molecular structures of CI, CII and CIII enzymes were indistinguishable; the enzymes were composed of two high molecular polypeptides 158,000 and 138,000 and several smaller subunits 99,000, 80,000, 78,500, 64,500, 52,000, 44,000, 32,000 and 24,000. Transcriptional activities of the chromatographically distinct forms of C polymerases were the same. The C enzymes exhibited striking affinity for homologous native A-T enriched DNA; Km values showed the greater number of binding and initiation sites localized in this template; therefore, A-T pairs are considered to be starter points for the transcription process catalysed by class C RNA polymerases.