Morphological phenotype of temperature-sensitive mutants of simian virus 40 in productive infection

Abstract

Temperature-sensitive mutants of simian virus 40 from the complementation groups I (viral-DNA positive and V-antigen positive), II (viral-DNA positive and V-antigen negative), and III (viral-DNA negative and V-antigen negative) were examined by electron microscopy for their ability to synthesize physical virus particles at the nonpermissive temperature (40°) in productive infection. Examinations of thin sections of infected cells revealed that all the group I mutants studied were not temperature-sensitive for the synthesis of physical virus particles in terms of the proportion of cells synthesizing virions, approximate number and mode of arrangement of virions in the virus-producing cells, and morphology of virions present in the cells. Representative mutants of the complementation groups II and III were temperature-sensitive for the synthesis of virions or virion-related structures. The virus particles of the group I mutants produced at 40°, in contrast to those produced at the permissive temperature (33°), were readily destroyed after lysing the cells by repeated freezing and thawing or by sonication, but the lysate still retained V antigen, the amount of which was similar to that in lysates from the mutant-infected cells at 33° and from wild-type-infected cells at 33 and 40°. Temperature-shift experiments suggested that: (1) The event that is temperature sensitive in a group I mutant infection occurs about the time of the appearance of new infectious virions, suggesting that the mutation affects the final stage of virus maturation; (2) the affected function of the group II mutant occurs at about 10 hr prior to the time of the appearance of new infectious virions at 33°, although the mutant employed may be regarded as a late mutant because of the heat lability of the virions produced at 33° and because viral DNA synthesis is normal at 40°; and (3) the group III mutant temperature presented suggest that the three genetically distinct groups of mutants represent three functionally distinct processes in the replicative cycle of simian virus 40.