The effects of several divalent cations on the activation or inhibition of RNA polymerases II

Abstract

Eukaryotic RNA polymerases II or B have been generally shown to be more active with Mn 2+ rather than Mg 2+ as the required divalent metal ion. However, very little was known about the activation or inhibition of RNA polymerases by metal ions other than Mg 2+ and Mn 2+. In this study the effects of several divalent cations were observed on in vitro transcription by highly purified RNA polymerases II from the mushroom Agaricus bisporus and calf thymus. Cobalt (II), Fe 2+, Mg 2+, or Mn 2+ may function as the divalent metal activator for RNA synthesis catalyzed by RNA polymerase II from calf thymus with the maximal activity observed using Fe 2+ as the activating metal ion. Of the 13 divalent cations used in this study, only Co 2+ or Mn 2+ can serve as the required divalent metal for RNA polymerase II from A. bisporus. Barium (II) had an apparent synergistic effect on the activation of RNA polymerase II from A. bisporus and calf thymus, and Sr 2+ exhibited a strong positive synergism on the activity of the mushroom enzyme. RNA polymerases II from both the mushroom and calf thymus were significantly inhibited by Be 2+, Cd 2+, Hg 2+, Ni 2+, and Zn 2+. A. bisporus RNA polymerase II was strongly inhibited by Cu 2+ and Fe 2+. The particularly potent metal inhibitor, Zn 2+, was shown to manifest competitive inhibition for both enzymes with respect to the substrates as determined with Mn-uridine triphosphate. Zinc (II) was also shown to manifest mixed inhibition with respect to the DNA template cofactor for both the calf thymus and mushroom RNA polymerase II.