Identification of temperature-sensitive mutants of vaccinia virus that are defective in conversion of concatemeric replicative intermediates to the mature linear DNA genome.

Pulsed-field gel electrophoresis was used to screen temperature-sensitive mutants of vaccinia virus for the ability to convert replicated viral DNA into mature linear 185-kilobase hairpin-terminated genomes. Of 30 mutually noncomplementing mutants tested, 5 displayed a temperature-sensitive defect in the resolution of the telomere fusion configuration within concatemeric replicative intermediates, resulting in a failure to convert such intermediates to the linear monomeric genome. Adjacent genomic units in the concatemeric arrays generated in these mutants were arranged in both tandem and inverted orientations. The observation that four of the five mutants had a severe general defect in the synthesis of the late class of viral proteins suggests that at least one late protein is directly required to resolve the telomere fusion intermediate to hairpin termini. The identification of such telomere resolution proteins should be facilitated by genetic and molecular characterization of resolution-defective mutants, such as C63, in which late protein synthesis is not severely affected.