The transforming activity of the cellular src (c-src) gene as well as of hybrid genes between viral and cellular src was tested by constructing derivatives of Rous sarcoma virus DNA in which all or part of the viral src gene (v-src) was replaced by the corresponding portion of the c-src gene. After these derivatives were introduced into chicken embryo fibroblasts by transfection, replication-competent virus was recovered, which induced the expression of p60 at a level equivalent to p6OV-SrC expression in cells infected with Rous sarcoma virus wild type. Replacement of the portion of the v-src gene, either upstream or downstream of the Bgl I site, with the homologous portion of the c-src gene resulted in fully transforming viruses. On the other hand, the virus stock obtained from cells transfected with Rous sarcoma virus DNA containing the entire c-src gene had a very low titer of focus-forming virus, while it contained a high titer of infectious virus. We present evidence that the rare small foci are formed by mutant viruses generated from the original c-src-containing virus. These results indicate that overproduction of the c-src gene product does not cause cell transformation, and that this proto-oncogene is subject to a relatively high rate of mutation when incorporated in a retrovirus genome, resulting in the acquisition of transforming capacity.
Rous sarcoma virus (RSV) (1) has been widely used for studies on viral carcinogenesis as a prototype of avian sarcoma viruses. The gene responsible for cell transformation by RSV is known as src; it codes for a phosphoprotein of about 60,000 daltons called pp6osrc (2, 3). src appears to be the transforming gene of another avian sarcoma virus, B.77 (4, 5), which was isolated by Thurzo et al. in 1962 (6). Fujinami and Inamoto (7) also obtained a similar sarcomagenic virus from a transplantable myxosarcoma in chicken. The tumor cells produced by Fujinami sarcoma virus (FSV) were shown to readily produce sarcomas in ducklings (8-11) before such a heterotransplantation was successful with RSV-induced tumors. However, FSV has been used in only a limited number of studies on cell transformation of cultured chicken and duck cells (11,12), and essentially no studies have been made on the nature of this virus.We report in this paper that one stock of FSV is profoundly different from RSV in its genomic structure despite its pathogenic similarity. The most striking feature of FSV is the absence of the src gene, which had previously been found in all other avian sarcoma viruses. Instead, the virus appears to contain a probable transforming gene linked to the structural protein gene known as gag, a feature that is more common to avian acute leukemia viruses or mammalian sarcoma-leukemia viruses.MATERIALS AND METHODS Cells and Viruses. Both chicken embryo fibroblasts and hatched chickens were obtained from group-specific antigennegative eggs supplied from SPAFAS (Norwich, CT The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. 搂1734 solely to indicate this fact.
In the avian system, RNA tumor viruses have been classified into three main groups: (i) sarcoma viruses, (ii) acute leukemia viruses, and (iii) lymphoid leukosis viruses (1). Fujinami sarcoma virus (FSV) (2) is a recently characterized, potent sarcoma-forming virus in chickens (3,4). FSV is defective in its replication and carries unique sequences of at least 3000 nucleotides in the middle of the genome flanked with helper viral sequences at both the 5' and 3' ends. Fujinami viral RNA was shown to be unrelated to src sequences of Rous sarcoma virus (RSV) by RNA fingerprinting and by hybridization experiments with DNA complementary to src (3, 4). pp60src, a phosphoprotein of 60,000 daltons coded by the src gene of RSV (5, 6), was not detectable in FSV-transformed cells; however, a unique protein of 140,000 daltons was precipitable from these cells by antisera against viral structural proteins coded by the gag gene of avian retroviruses. This gag-related polyprotein, p140, suggested to be responsible for transforming capacity of this virus, has an associated protein kinase activity that phosphorylates tyrosine residues on immunoglobulin heavy chain, casein, and p140 itself (7).In this paper we report the preparation of DNA complementary to FSV-specific nucleotide sequences and the distribution of these sequences among avian and mammalian retroviruses. The results indicate that RNAs of PRCII sarcoma virus (8)
33 Our recent experiments, with improved experimental methods, do not support our earlier conclusion3 that TPN is also required for cyclic photophosphorylation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations鈥揷itations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.