NEW CLASSES OF VIABLE DELETION MUTANTS IN THE EARLY REGION OF POLYOMA-VIRUS

Viable mutants of polyoma virus were isolated which have deletions in defined parts of the early region of the genome. One class of mutants has deletions (less than 1% of viral genome length) located between 71.5 and 73.5 on the physical map of polyoma virus DNA, near the origin of replication. These mutants appear to grow and to transform [rat embryo] cells in a manner indistinguishable from wild-type virus. A 2nd type of mutant with deletions (about 2% of viral genome length) located between about 88 and 94.5 units on the physical map of polyoma virus DNA have altered transformation properties. One of the latter (which maps between 88 and 91.5 units) has altered growth characteristics, whereas another (which maps between 91.5 and 94.5 units) resembles wild-type virus in its growth properties. The regions with deleted sequences were defined by cleaving mutant DNA with restriction endonucleases and analyzing pyrimidine tracts.