Temperature-sensitive mutants of vaccinia virus. I. Isolation and preliminary characterization.

Fifty-seven temperature-sensitive (ts) mutants of a neurotropic variant of vaccinia virus were obtained. A comparison of the effectiveness of 6 different mutagens showed that in in vivo experiments nitrosomethylurea induced 10%, nitrosoguanidine 8%, and bromodeoxyuridine 2.5% ts mutants. In vitro, at the same degree of inactivation, UV irradiation, hydroxylamine and nitrous acid induced 2.5% ts mutants. Out of 49 mutants studied, 27 had a DNA+ phenotype, 19 a DNA+/-and 3 a DNA- phenotype. Under permissive conditions, two thirds of all the mutants tested formed thermolabile virions. In experiments on genetic recombination, the recombination frequency between different pairs was from 2.8 to 57%. Seven of the mutants were plotted on the virus genetic map in a certain sequence.