Ribonucleases of Rous sarcoma virus

Abstract

Purified Rous sarcoma virus and avian leukosis virus preparations contain ribonucleases which hydrolyze polyuridylic acid (Poly U), polyadenylic acid (Poly A) and the double-stranded hybrid of poly U and poly A (Poly A:Poly U). The ribonucleases become soluble when the virus is dissociated with a neutral detergent (Brij 35), mercaptoethanol, and urea. Carboxymethyl cellulose chromatography partially separates the ribonucleases into two activity peaks; one for Poly U and the other for Poly A or Poly A:Poly U. The chromatographed fractions are further purified by gel filtration yielding approximate molecular weights of 13,000 for the enzymes. The partially purified enzyme preparations also digest the viral RNA in disrupted virions, but not the viral DNA in the disrupted virions synthesized by reverse transcriptase of the virus. The intact virus in solution shows a very high ribonuclease activity toward Poly U, but not toward Poly A or Poly A:Poly U. The viral RNA in the intact virus is stable during a prolonged incubation in spite of the fact that the virus contains the ribonucleases capable of digesting the RNA. Moreover, the viral RNA in the disrupted virions is also stable when incubated alone, although it becomes digested when the viral enzyme preparation is added. These observations suggest that the ribonuclease which prefers Poly U is located on the surface, and that the other ribonucleases which prefer Poly A and Poly A:Poly U reside between inner and outer membranes of the virion. The origin of the ribonucleases in Rous virus is not clear. From chick embryo fibroblasts, ribonucleases for Poly U, Poly A and Poly A:Poly U can be isolated with carboxymethyl cellulose chromatography. The ribonuclease activity for the double-stranded RNA is low in these preparations. After transformation by Rous virus, the chick cells demonstrate all these ribonuclease activities with a considerable increase in the activity for Poly A:Poly U. The ribonuclease activities of purified Rous virus resemble those of the transformed cells.