The nucleic acid from avian myeloblastosis virus compared with the RNA from the Bryan strain of Rous sarcoma virus.

Abstract

This paper describes properties of the nucleic acid isolated from the avian myeloblastosis virus (AMV) and compares this nucleic acid with the RNA from the Bryan strain of Rous sarcoma virus (RSV) and its helper virus, Rous associated virus (RAV). The Bryan strain of RSV is defective' and infected cells do not produce mature RSV unless simultaneously infected with an avian leukosis virus such as Rous associated virus (RAV) which functions as helper virus and presumably provides a protein coat for RSV.2 For this reason all preparations of RSV contain a helper virus which is usually present in 4-10 times higher concentrationl 3' 4 of infectious particles than RSV and which has coat properties indistinguishable from those of RSV. Because of the similar properties, RSV has not been separated from its helper virus.4 A recent report from this laboratory5 describes the purification of the mixture designated RSV + RAV and the isolation and preliminary characterization of the viral RNA. Avian myeloblastosis virus, like RAV, is an avian leukosis virus and the two are closely related biologically. Both will function as helper viruses for RSV,2 6 interfere with RSV,4 and produce tumors in chickens. They differ in specific antigens, and only AMV produces acute myeloblastic leukemia.7 The intact virus particles have been shown to have similar morphology, chemical composition, and physical properties.7' 8 Because of the close relation, it might be expected that the two would have similar nucleic acids. However, previous reports9' 10 describe only lowmolecular-weight RNA isolated from AMV, and each of several reports-3 reveals a different RNA base composition. In the present study we find the nucleic acids of AMV and RSV + RAV to be single-stranded RNA, indistinguishable in sedimentation behavior and change in conformation with change in salt concentration and very similar in base composition. Methods and Materials.--Viruses: An AMY strain, kindly supplied by Dr. P. K. Vogt, belonging to the BAI strain A and to the B classification of Vogt,7 and RSV + RAV-86 were used. Production of AMV: Chick embryos on the 12th day of incubation were inoculated intravenously'4 with 104 converting units5 of AMY and allowed to hatch. The chicks that showed a very high leukemic cell count (5 X 105 or more per mm3) in the peripheral blood 10 days after hatching were exsanguinated by cardiac puncture. The blood was collected into hepariin and centrifuged at low speed to pack the cells. The leukemic myeloblasts forming the upper two thirds of the packed cell layer were distinctly separated from the lower layer of erythrocytes. The leukemic cells were isolated and resuspended at a concentration of 1-5 X 106 cells per ml in nutrient medium.5 Ten ml of cell suspension in a 100-mm plastic tissue culture dish was incubated at 40?C in a humidified incubator flushed with a C02-air mixture to maintain the culture pH around 7.3. The cells did not attach to the floor of the plate. At approximately 12-hr intervals for 48-96 hr the cells were removed from the medium by low-speed centrifugation and resuspended in fresh medium. The medium recovered after each period of incubation was centrifuged a second time at 2,000 X g for 15 min to remove cell debris and was then frozen at 80?C until used for virus purification at a later time. Such medium contained about 105 converting units per ml.