Abstract
A mutant derived from a temperature-sensitive mutant of Rous sarcoma virus ( tsNY68 ) which showed extremely low infectivity was characterized. Infection of chicken embryo fibroblast cells with the mutant, TK15 , induced two types of transformants, mutant-producing 15c (+) and nonvirus -producing 15c (-) transformants. 15c (+) cells expressed all four viral genes normally and produced a normal level of virus particles. No complementation was observed between the mutant and avian leukosis viruses. However, when 15c (+) cells were cocultured with nonvirus -producing cells transformed by Y73, a replication-defective avian sarcoma virus, a high titer of Y73 virus was recovered. From its biological properties, the mutant seemed to have a defect(s) outside the viral genes. Biochemical analysis of the TK15 mutant (T. Koyama , F. Harada, and S. Kawai , J. Virol. 51:154-162, 1984) revealed that it had a defect in packaging its own genomic RNA. During replication of TK15 virus, the TK15 mutant appeared to segregate at high frequency more defective variants that induced 15c (-) transformants, in most of which only the src gene was expressed. The mechanism for the segregation of 15c (-) transformants is discussed with respect to the defect of the mutant.