Temperature-sensitive mutants of avian sarcoma viruses: Genetic recombination with wild type sarcoma virus and physiological analysis of multiple mutants

Abstract

Genetic recombination experiments have been carried out to analyze the genotype of two “coordinate” ts mutants of the avian sarcoma viruses, LA334 and LA338. Recombination between Prague strain B of Rous sarcoma virus (PR-B) and LA334, resulted in progeny consistent with the mutant having two lesions, one affecting the maintenance of transformation, the other replication of infectious virus. LA338 appears to possess at least three mutations; one is similar to that in LA334 and affects the maintenance of transformation; a second prevents the synthesis of infectious virus at the restrictive temperature; the third affects an early function necessary to initiate transformation. This early defect can be complemented by and is lost on recombination with leukosis viruses. Temperature shift experiments have confirmed that the defective replication functions in LA334 and LA338 are late and reversible. They can both be complemented by leukosis viruses, but appear to affect different stages in replication; in fluorescent antibody studies at the nonpermissive temperature, LA334-infected cells contained normal levels of the major viral structural polypeptides, whereas LA338-infected cells contained reduced amounts. High frequency recombination was observed between host range and transformation markers. The significance of these frequencies is discussed.