Variations in sarcoma and leukemia virus activity in somatic cell hybrids

Abstract
Somatic cell hybrids have been produced in hypoxanthine‐aminopterin‐thymidine (HAT) selective medium by fusion of mouse cells deficient in hypoxanthine‐guanine phosphoribosyl transferase (HGPRT), shedding Rauscher leukemia virus and a hamster cell deficient in thymidine kinase (TK) carrying the defective murine sarcoma virus (MSV) genome. Clones were isolated that produced sarcoma and leukemia virus at substantially equivalent titers, a 100‐fold excess of sarcoma virus, or just leukemia virus. Eight clones were analyzed by isoelectric fractionation and all found to possess HGPRT and adenosine kinase (AK) of hamster origin. Six of these clones also produced AK characteristic of the mouse parent. The production of excess sarcoma virus by some clones and the lack of sarcoma virus expression in cells possessing hamster genetic material are discussed in terms of integration of sarcoma virus in host‐cell chromosomes.