Analysis of the Defectiveness of Rous Sarcoma Virus, Ii. Specification of RSV Antigenicity by Helper Virus

Abstract

The high-titer strain of Rous sarcoma virus (RSV) is defective, in the sense that it is unable to spawn infectious progeny without the intervention of a helper virus.1 The first helper virus to be discovered was isolated from a stock of the high-titer strain of RSV, and has been named Rous associated virus, or RAV.2 RAV has all the physical and biological attributes of viruses of the avian leukosis complex and is therefore considered a member of this group of viruses. In keeping with this classification, all avian leukosis viruses tested to date have been found to be active as helper viruses for RSV.The precise role of helper virus in activating RSV has not yet been defined, but some possibilities for the helper function can be eliminated by considering those functions which RSV can carry out alone. Thus, RSV can effect the malignant transformation of chick embryo cells to sarcoma cells without the aid of helper virus. The sarcoma cells retain their characteristic morphology through many divisions. Since the transformed cells produce no mature RSV, they are called nonproducer, or NP, cells. If at any time during extended periods of cultivation, NP cells are superinfected with helper virus, a high proportion, if not all, of the NP cells will produce RSV. This demonstrates that the RSV genome is replicated in the NP cells without the aid of helper virus and that the helper virus is required only for the maturation of RSV. The most characteristic feature of virus maturation is the enclosure of the viral genome by an outer coat of protein or lipoprotein, which endows the virus with the property of infectiousness. The failure of the replicating RSV genome to mature into infectious virus suggests that the defect of RSV derives from its inability to direct synthesis of the virus-specific portion of its own outer coat. This suggestion gains support from the immunological identity of the high titer strain of RSV with its indigenous helper virus, RAV,3 since the inability of RSV to synthesize its own coat would require that RAV direct coat synthesis for both viruses.Two predictions, both of which are readily amenable to experimentation, arise from the concept that RSV is wholly dependent upon helper virus for production of the virus-specific portion of its coat. The first prediction is that NP cells contain no virus-specific coat antigens. NP cells should therefore be incapable either of absorbing RSV-neutralizing antibodies from antisera or of stimulating the synthesis of neutralizing antibodies when inoculated into chickens. The second prediction is that, if antigenically different helper viruses are employed, the antigenic structure of the virus-specific coat protein of RSV should be that of the helper virus used. Both predictions are explored in the experiments reported here and both are borne out by the results.Material and Methods.-Terminology and notation: "Activation" refers to the process, mediated by helper virus, through which RSV becomes an infectious particle. "Virus-specific coat antigens" are defined here as...

Cytochemistry, Cytogenetics and Ultrastructure of Hamster Tumour Cells Carrying Mouse Sarcoma Viral Genome (HT-1 Cells)

“…This MSV had the immunological characteristics of the helper leukaemia virus used and could induce both transformation of normal MEF in vitro and the production of sarcomas in inoculated animals. It was apparent then, that the HT-1 cells were carrying the MSV genome though initially not producing the virus-a state which could be compared with that of the non-producing (NP) cells previously described for Rous sarcoma virus (RSV) (Hanafusa et al, 1964 (Sarma et al, 1965). Recent trans-species rescue of the MSV genome from HT-1 cells by feline leukaemia virus (Sarma et al, 1970) Since most HT-1 cells grew in suspension, the cells had to be spun down for the preparation of spreads on glass slides.…”

The early history of tumor virology: Rous, RIF, and RAV

“…The possible presence of viral coat antigen was also tested by inoculating NP cells into chickens to produce tumors and examining them for neutralizing antibodies. The inoculation of relatively small numbers of intact NP cells into chickens induced visible tumors within 5 d, which continued to grow for approximately 12 d, when they started to regress (46). The regression of the NP tumors is presumably the result of an immunological reaction to antigens in the tumor cells.…”

“…The NP cells were incapable of either absorbing RSV-neutralizing antibodies from antisera or of stimulating the synthesis of neutralizing antibodies when inoculated into chickens, indicating that the virus-specific coat protein is that of the helper virus used (46). The possible presence of viral coat antigen was also tested by inoculating NP cells into chickens to produce tumors and examining them for neutralizing antibodies.…”

Enhanced Replication of Newcastle Disease Virus in Cell Culture Co-infected with Certain Other Viruses

“…However, they do so when they are co-infected with certain chicken tumor viruses [15]. The Rous virus is defective in genetic information for the synthesis of viral coat protein, and this information is contributed by the co-infecting helper virus [16].…”