A map of temperature-sensitive mutants of simian virus 40.

Temperature-sensitive mutants of simian virus 40 (SV40), representing each complementation class, have been mapped by marker rescue with Endo R fragments of wild-type SV40-DNA. The 41 mutants mapped cover most of the genome, but there is a notable absence of mutants mapping between 0.43 and 0.85 map-units. Mutants which are defective in viral DNA synthesis (tsA mutants) all map in the “early” region of the genome; 12 of 13 such mutants are clustered in about one-fourth of the “early” region between 0.32 and 0.43 map-units. Mutants in complementation classes defective in a late function map in the “late” region and also show clustering: eight of nine B mutants map between 0.94 and 0.06 map-units, all C mutants map between 0.06 and 0.11 map-units, and seven of eight BC mutants map between 0.11 and 0.17 map-units. D mutants, which are thought to be defective in virus uncoating at high temperature, all map between 0.85 and 0.94 map-units, i.e., in a small segment of the “late” region. Therefore, the genomic segment associated with the defect of D mutants likely codes for a virion protein. One C mutant proved to be a double mutant with one mutation in the B region and another in the C region, both mutations being required for the tsC phenotype. On the basis of the mapping data and prior complementation tests we suggest that B, C, and BC mutations are in one cistron, complementation occurring at the protein level.