Multiple Forms of Nuclear Ribonuclease H from Tetrahymena pyriformis

Abstract

Three types of ribonuclease H [RNA:DNA hybrid ribonucleotidohydrolase] from the isolated macronuclei of T. pyriformis GL, were partially purified and characterized. They were eluted at .apprx. 0.15 M, 0.3 M and 0.4 M of ammonium chloride in phosphocellulose chromatography, and termed H-1, H-2 and H-3, respectively. The partially purified specifically hydrolyzed the RNA moiety of the RNA .cntdot. DNA hybrid. Neither the DNA moiety of the RNA .cntdot. DNA hybrid nor the RNA molecule dissociated by heat from the RNA .cntdot. DNA hybrid was hydrolyzed by these enzymes. The enzymes were most active at pH 8.5-9.0. They required divalent cations such as Mg2+ or Mn2+ for their activities. The optimal concentrations of these cations were different for these enzymes. The mode of cleavage by these enzymes was endonucleolytic, producing mostly oligonucleotides and a small amount of mononucleotides which possess 3''-hydroxyl and 5''-phosphate termini.