Physical map of the Kirsten sarcoma virus genome as determined by fingerprinting RNase T1-resistant oligonucleotides
Journal of Virology
From analysis of the large RNase Tl-resistant oligonucleotides of Kirsten sarcoma virus (Ki-SV), a physical map of the virus genome was deduced. Kirsten murine leukemia virus (Ki-MuLV) sequences were detected in Ti oligonucleotides closest to the 3' end of the viral RNA and extended approximately 1,000 nucleotides into the genome. The rat genetic sequences started at this point and extended all the way to the very 5' end of the RNA molecules, where a small stretch of Ki-MuLV sequence was
... sequence was detected. By comparison of the fingerprints of Ki-SV RNA and the RNA of the endogenous rat src genetic sequences, it was found that more than 50% of the Ti oligonucleotides were similar between Ki-SV and the endogenous rat src RNA, suggesting an identical primary nucleotide sequence in over 50% of the viral genomes. The results indicate that Ki-SV arose by recombination between the 5' and 3' ends of Ki-MuLV and a large portion of the homologous sequences of the endogenous rat src RNA. Kirsten and Harvey sarcoma viruses (Ki-SV and Ha-SV, respectively) were isolated by inoculation of murine leukemia viuses (MuLV's) into various strains of rats (11, 13) . Although the original isolates were mixtures of leukemia and sarcoma viruses, subsequent studies clearly showed that the viruses that induce solid tumors in animals and transform fibroblasts in tissue culture (FT') are the replication-defective components of the leukemia-sarcoma complexes with smaller genomes (1, 15, 16, 22) . Studies in this laboratory (4, 22, 23) and recently by other investigators (2) have demonstrated that the genomes of these two sarcoma viruses contain sequences homologous to the leukemia viruses from which the sarcoma viruses were derived and, in addition, sequences derived from rat genetic information. Recent studies have revealed that this rat genetic information, which is expressed in a variety of rat cells as RNA, has all of the characteristics of an endogenous type C virus (19, 24, 27): (i) the genetic information exists as multiple copies (20 to 40) per haploid rat cell genome; (ii) it is inducible with halogenated pyrimidines to high levels of expression; (iii) it is specifically packaged by type C helper viruses; (iv) the subunit size is approximately 30S, and it forms dimer structures of approximately 60S; and (v) it is transmissible to some host cells (Scolnick, unpublished data). Since the sarcomagenic potential of Ki-SV and Ha-SV seems to have been associated with the acquisition of this class of endogenous type C virus sequences and for simplicity, we shall hereafter in this paper refer to this virus RNA as the endogenous rat "sarcoma" virus RNA, although the sarcomagenicity of this endogenous virus has not yet been conclusively demonstrated. In the present paper, we attempt by fingerprinting the viral RNA in a two-dimensional gel electrophoresis system, to: (i) characterize the endogenous sarcoma virus RNA, (ii) compare the homologous sequences between Ki-SV and the endogenous sarcoma virus and between Ki-SV and Ki-MuLV, and (iii) map the rat and the Ki-MuLV sequences in the Ki-SV genome. A possible mechanism for the generation of Ki-SV and a functional implication of the organization of the viral genome will be discussed.