摘要：

Theonly knownproduct oftheSnyder-Theilen strain offeline sarcoma virus (ST-FeSV) isa85,000-dalton pro- tein, designated STP85, that contains feline leukemia virus gag geneencoded proteins (p15, p12, andafragment ofp30) anda sarcoma virus-specific polypeptide. Antibodies directed against thelatter immunoprecipitated a92,000-dalton phosphoprotein (NCP92)expressed atlowlevels innormal feline embryo fi- broblasts aswell asinfeline cells ofepithelial orlymphoid or- igin. Normal cellular proteins crossreactive withSTP85were also detected incell lines fromvarious other mammalian species. These results suggest that theST-FeSV sequences en- coding forthesarcoma virus-specific domain ofSTP85origi- nated fromanevolutionarily conserved cellular geneexpressed incells ofindependent differentiation lineage. Immunopre- cipitates containing ST-FeSV P85exhibited aprotein kinase activity that specifically phosphorylated tyrosine residues. The physiological significance ofthis finding isillustrated bythe finding thatphosphotyrosine isanintrinsic component ofST P85. Furthermore, 5-to10-fold higher levels ofthis unusual phosphorylated aminoacid werepresent inST-FeSV transfor- mantsthan inuninfected control cells. Phosphorylation ofty- rosine residues appears tobeassociated with cellular transfor- mation caused byRoussarcoma virus andAbelson murine leukemia virus. Thus, independent transforming virus isolates frombirds, mice, andcats mayutilize commonpathways in exerting their oncogenic potential. Feline sarcoma viruses (FeSVs) have beenshown tobeetio- logically associated with spontaneous fibrosarcomas ofyoung cats(1). Todate, three independent isolates ofFeSV-the Snyder-Theilen (ST) (2), theGardner-Arnstein (GA) (3), and theMcDonough (SM)(4)strains-have beenbiologically characterized. Eachhasbeenshown totransform fibroblasts intissue culture andtorequire areplication-competent helper

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