Magnesium and Manganese Specific Forms of Soluble Liver RNA Polymerase

Abstract

Widnell and Tata¹ and others^2,3 found that the RNA synthesizing properties of isolated mammalian cell nuclei vary depending on whether the assay system contains Mg⁺⁺ (in the absence of ammonium sulphate) or Mn⁺⁺ and ammonium sulphate. It is not known whether the differential effect is caused by the presence of different species of RNA polymerase or by a salt effect which may alter the action of inhibitory substances associated with nuclear DNA⁴ or with the polymerase^5–7. Recently, we showed that liver nuclei contain a large amount of soluble RNA polymerase which can be released at 0° C without concomitant release of DNA or lysis of nuclear membranes⁸. During the purification of this enzyme, we observed that the ratio of the RNA polymerase activity measured in the presence of Mn⁺⁺ (but no ammonium sulphate) to that determined in the presence of Mg⁺⁺ was not constant among the various enzyme fractions. This and other observations described here strongly suggest that cell nuclei of liver and ventral prostate have at least two forms of RNA polymerase with different specificities toward DNA templates and requirements for divalent cations.