The transforming gene product of the Moloney murine sarcoma virus (M-MSV) genome has been difficult to study because of its low immunogenicity and low level of synthesis. A DNA clone of the viral genome will be manipulated to fuse this viral src gene to the gag gene of M-MSV. The resulting fused polyprotein will be of great utility in studying the src gene because of its immunoprecipitation via its gag antigens, and because of its high levels of synthesis. A second project will undertake the creation of novel sarcoma virus genomes by fusing the left genomic end of the Harvey MSV DNA genome, which contains a strong transcriptional promoter, to cDNA transcripts of the mRNAs of a chemically transformed cell. The successful creation of novel sarcoma viruses will provide a new way for the molecular cloning and analysis of cellular transforming genes.