A Single Subunit from Avian Myeloblastosis Virus with Both RNA-Directed DNA Polymerase and Ribonuclease H Activity

Abstract

Two structurally distinct forms of RNA-directed DNA polymerase from avian myeloblastosis virus were resolved by chromatography on phosphocellulose and purified. In addition to RNA-directed DNA polymerase activity, both enzymes had ribonuclease H (RNase H) activity, which degraded the RNA moiety of RNA.DNA hybrids. As determined by sodium dodecyl sulfate-polyacrylamide disc-gel electrophoresis, one form had two subunits, alpha (alpha) and beta (beta), with molecular weights of 65,000 and 105,000, respectively. The other had a single subunit, alpha, with a molecular weight of 65,000. The sedimentation coefficients of alphabeta and alpha, determined by glycerol gradient centrifugation in 0.35 M KCl, were 7.8 S and 5.2 S, respectively. Both enzymes had similar antigenic determinants and could not be distinguished by a differential response to several different RNA and DNA templates. We suggest that alpha, which contains both RNA-directed DNA polymerase and RNase H activity, is derived by dissociation of alphabeta; the function of the beta subunit is unknown.