Cellular information in the genome of recovered avian sarcoma virus directs the synthesis of transforming protein.

Abstract

Recovered avian sarcoma viruses, whose sarcomagenic information is largely derived from cellular sequences [Wang, L.-H., Halpern, C. C., Nadel, M. & Hanafusa, H. (1978) Proc. Natl. Acad. Sci. USA 75,[5812][5813][5814][5815][5816], produce the transforming protein p6osrc in infected cells, in amounts comparable to the amount found in cells transformed by standard strains of avian sarcoma virus. Though displaying some virusspecific differences in electrophoretic mobility, p6Osrcs from these viruses are similar to those of other avian sarcoma virus strains by the criteria of (i) antigenicity, (ii) partial proteolysis mapping, and (iii) association with protein kinase activity. We also find that p6Osarc, a protein present in normal cells at a low level, is associated with a protein kinase activity, and thus it too is similar by the above criteria to p6osrc of avian sarcoma virus.Possible causes for the pathogenicity of p6Osrc are discussed in light of these similarities.The src gene of avian sarcoma viruses (ASVs) is responsible for the ability of these agents to induce tumors in chickens and to transform fibroblasts in tissue culture (1, 2). This gene is not required for virus replication, because transformation-defective (td) mutants of ASV, lacking all or a part of src, are still capable of normal growth (1-3). The identification of src-related sequences in the genome and cytoplasmic RNA of normal uninfected chicken cells has led to the definition of a presumptive genetic element in normal cells denoted sarc (4-6).Erikson and coworkers have identified a protein (7), called p6Osrc, that is encoded by the src region of the ASV genome (8).It is a phosphoprotein (9) of 60 kilodaltons (kDal) that is found closely associated with, and may be identical to, a protein kinase activity (10-12). An antigenically and structurally related protein has been found in small amounts in immunoprecipitates of normal chicken cells (13). Because this protein is presumed to be coded by the endogenous sarc gene, it has been denoted p6Osarc. However, no associated protein kinase activity was detected (13).We have reported the isolation of a number of ASVs from chicken tumors produced after long latent periods following injection of certain td mutants of the Schmidt-Ruppin strain of Rous sarcoma virus (SR) of subgroup A (SR-A) (14). Virus recovered from these tumors had regained the capacity to transform cells in culture and to rapidly induce tumors in chickens at the site of injection. The genomes of these recovered avian sarcoma viruses (rASVs) had acquired src-specific genetic information (15,16). It is likely that the recovered sarcomagenic information was obtained through a recombination event between the parental td virus and endogenous sarc sequences of normal cells (16).We report here that rASVs possess information directing the production of p6Osrc, and show it to be enzymatically and structurally similar to the p6Osrc of the SR-A strain of ASV. In addition we show that p6Osarc of normal cells shares both structural and en...

A normal cell protein similar in structure and function to the avian sarcoma virus transforming gene product.

“…In addition, as others have reported (16,25), we find an occasional TBR that exhibits a similar wide immunoreactivity for src and src-related proteins. It is our experience that such crossreacting rabbit serum appears in less than 5% of our tumor-bearing animals.…”

“…This fact, coupled with the similarity in structure of the cellular and viral gene products and the nature of the transforming viruses recovered by 25), supports the possibility that the phosphoprotein products of both the normal cellular gene and the viral gene have identical functions. It follows then that the biochemical events in ASV-induced oncogenesis may be qualitatively identical to those in normal cells but perhaps occur to a greater degree, as the result of pp6Osrc expression, to produce the transformed phenotype.…”

“…Previous studies from this laboratory (15,20) and others (16,25) have demonstrated that the viral pp6Osrc and the normal avian and mammalian pp6Osarc proteins are similar, although not identical, in primary structure. Because the normal cell and viral proteins are phosphorylated, it is possible that phosphorylation-dephosphorylation modifications of the src and src-related polypeptides may be involved in their functional control.…”

Characterization of sites for tyrosine phosphorylation in the transforming protein of Rous sarcoma virus (pp60v-src) and its normal cellular homologue (pp60c-src).

“…Uninfected vertebrate cells contain a similar protein [pp6Ocrc (8)(9)(10)(11)(12)]. Both pp6Ov-rc and pp60c-*c are phosphorylated on serine and tyrosine; these phosphorylations may regulate the enzymatic activity of the proteins.…”

“…It is likely that these phosphorylations serve to regulate the function(s) of pp60v87c and pp6COr. We The transforming gene (v-src) of Rous sarcoma virus (RSV) encodes a 60,000-dalton protein (pp6V-rC) that is capable ofphosphorylating tyrosine in a variety of protein substrates (1-7).Uninfected vertebrate cells contain a similar protein [pp6Ocrc (8)(9)(10)(11)(12)]. Both pp6Ov-rc and pp60c-*c are phosphorylated on serine and tyrosine; these phosphorylations may regulate the enzymatic activity of the proteins.…”