Polyoma virus-transformed cells produce transforming growth factor(s) and grow in serum-free medium

Vaccinia virus temperature-sensitive (ts) mutants were isolated after nitrosoguanidine mutagenesis. A number of these mutants exhibited host range temperature sensitivity in that the efficiency of plaque formation at the nonpermissive temperature was poorer on chick cells than on hamster or human cells. Forty-two mutants were assigned to 23 different complementation groups on the basis of complementation and the efficiency of apparent recombination at the nonpermissive temperature. Recombination frequencies were also determined from mixed infections carried out at the permissive temperature and it was confirmed that mutants within the same complementation group recombined less efficiently with each other than mutants belonging to different groups. Mutants from two of the largest groups could be tentatively ordered on linear intragenic maps that spanned 0.8 and 2 recombination units. Moreover, from intergenic crosses between mutants in 14 different complementation groups, a linkage map spanning 66.3 recombination units, was derived. This study illustrates the feasibility of two-factor recombination mapping of poxvirus mutations and provides genetic data that should be of relevance in further analysis of the is mutations.