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

Abstract A temperature-sensitive ( ts ) mutant of murine cytomegalovirus, ts 2l, lacks pathogenicity for suckling mice. Revertants ( rev 2l) of ts 21 which could replicate at nonpermissive temperature remained attenuated, suggesting the presence of a temperature-independent factor(s) for the attenuation. Coinfection of ts 21 with its parental wild-type ( wt ) generated recombinant-type progenies ( rec 2lw) which lacked temperature sensitivity and were still attenuated. The results indicate that ts 2l harbors at least two mutations and the mutation(s) in pathogenicity exists independently of the ts mutation(s).