The Moloney sarcoma virus genome consists of two parts - a sarcoma specific portion of about 1,600 nucleotides located most likely near the 3' end of the MSV genome (approximately 900 bases from the 3' end) and in a single unique stretch - and a common part of 4,000-5,000 nucleotides located at the 5' region of the MSV genome and including a stretch of 600-900 nucleotides at the 3' far end of the genome. The sarcoma specific sequences can be found in a single copy on a discrete mouse chromosome (most likely 8, 11, or 12). The common sequences can be found in multiple poorly related copies (5-8) in mouse chromosomes but no attempt has been made yet to localize the involved mouse chromosomes. Work to localize the Moloney sarc integration sites in homologous and heterologous host DNA is currently in progress. In addition work to localize sarc on different cellular mRNA site classes is in progress. BIBLIOGRAPHIC REFERENCES: Frankel, A.E., Haapala, D.K., Neubauer, R.L. and Fischinger, P.J.: Elimination of the sarcoma genome from murine sarcoma virus transformed cat cells. Science 191: 1264-1266, 1976. Frankel, A. E., and Fischinger, P. J.: Rate of divergence of cellular sequences homologous to segments of Moloney sarcoma virus. J. Virol. 21: 153-160, 1977.