Isolation and Characterization of Thermosensitive Mutants from Kilham Rat Virus, a Rodent Parvovirus

Thermosensitive mutants were isolated from nitrous acid-treated Kilham rat virus (KRV). At a restrictive temperature (39.5 °C), the mutants tested did not produce appreciable amounts of infectious particles, haemagglutinin or progeny single-stranded DNA. Virus antigen accumulation as detected by immunoperoxidase was reduced. Complementation tests revealed two distinct groups. The three members of complementation group 1 synthesized normal amounts of replicative forms but were restricted in single-stranded DNA production and capsid protein expression, exhibiting phenotypes compatible with cap mutations. The sole representative of group 2, KRV ts6, failed to accumulate replicative forms, displaying a rep- phenotype. These mutants provide new tools to test the role of viral products in the biology of autonomous parvoviruses.