Complementation between temperature-sensitive (ts) and host range nontransforming (hr-t) mutants of polyoma virus

Two major classes of polyoma mutants are defective in cell transformation: early temperature-sensitive mutants of the tsA type which are defective in viral DNA synthesis and transformation at 39 degrees, but not at 32 degrees; and host range nontransforming (hr-t) mutants which fail to transform at either temperature. Mixed infection of mouse 3T3 cells by hr-t mutants and early tsA-type mutants results in enhanced growth of the tsA-type mutants at 39 degrees, indicating that the hr-t mutants can supply the early viral function required for viral DNA synthesis. The hr-t mutants also complement late is mutants which fail to produce infectious progeny at 39 degrees because of alterations in the 45,000-dalton major virion protein. Mixed infection of hamster BHK or rat Y1 cells by hr-t and tsA-type mutants results in efficient transformation at 39 degrees, indicating that the two classes of mutants can complement for transformation. No complementation is observed in pair-wise crosses among the early tsA-type mutants alone. The tsA-type mutants are located in the distal portion of the early region of the polyoma genome [Miller, L. K., and Fried, M. (1976) J. Virol. 18, 824-832]. The hr-t mutants are located in the proximal portion [Feunteun, J., Sompayrac, L., Fluck, M., and Benjamin, T. (1976) Proc. Nat. Acad. Sci. USA]. These results suggest that the early region of the polyoma genome is divided into two functional regions which can complement for transformation. The ts3 mutant of polyoma is located in the proximal portion of the late region.