Poly(A) synthesis by RNA polymerase II from rat liver

Multiple forms of DNA-dependent RNA polymerase were resolved by DEAE-Sephadex chromatography. In addition to RNA polymerases, an active poly(A) polymerase was also fractionated. RNA polymerases were examined for their capacity to synthesize poly(A). None of the freshly prepared enzymes could efficiently make poly(A) in presence or absence of exogenous primers. However, “aging” of polymerase II by simple incubation at 37°C resulted in the loss of RNA polymerizing activity with a corresponding increase in poly(A) synthesizing activity. Transformation of RNA polymerase to poly(A) polymerase resulted in reduced capacity to transcribe native DNA and altered chromatographic behavior. The results suggest that subunits of polymerase II obligatory to DNA-dependent RNA synthesis were degraded by “aging” and that a stable subunit of the RNA polymerase could preferentially make poly(A).