Independent existence of mutations responsible for temperature sensitivity and attenuation in a mutant of murine cytomegalovirus

A temperature-sensitive ( ts) mutant of murine cytomegalovirus, ts2l, lacks pathogenicity for suckling mice. Revertants ( rev2l) of ts21 which could replicate at nonpermissive temperature remained attenuated, suggesting the presence of a temperature-independent factor(s) for the attenuation. Coinfection of ts21 with its parental wild-type ( wt) generated recombinant-type progenies ( rec2lw) which lacked temperature sensitivity and were still attenuated. The results indicate that ts2l harbors at least two mutations and the mutation(s) in pathogenicity exists independently of the ts mutation(s).