The ts59 mutant of polyoma virus is blocked in a late step of infection at the restrictive temperature. Cellular and viral DNA synthesis proceed normally in ts59-infected cells at the restrictive temperature, but infectious progency virus particles are not assembled. The ts59 mutant complements early tsA mutants in mixed infection, and the temperature-sensitive mutation maps in the late region of the polyoma genome. The infectivity of ts59 virions is much heat labile than wild-type polyoma. All three nonhistone capsid proteins of ts59, VP1 (45,000 daltons) and the overlapping proteins VP2 (30,000 daltons) and VP3 (20,000 daltons), show altered mobilities when analyzed by SDS-polyacrylamide gel electrophoresis. The tryptic peptide patterns of all three ts59 virion proteins also differ from the tryptic peptide patterns of wild-type proteins. Analysis of the ts59 proteins synthesized in vitro and in infected cells suggests that the alterations in the ts59 virion proteins are caused by differences in primary structure rather than by post-translational modifications. The capsid proteins of convertant virions produced by marker rescue of the ts59 temperature-sensitive mutation, using various restriction endonuclease fragments of wild-type DNA, have been analyzed. Results of these studies suggest that (i) 26 map units is the furthest point, in a clockwise direction on the genetic map, that the information for the C-terminus of VP1 can be from the Eco·R1 cleavage site; (ii) the N-terminal end of VP2 extends beyond the N-terminal end of VP3; (iii) the temperature-sensitive phenotype of ts59 is correlated with a peptide alteration common to VP2 and VP3. The ts59 mutant contains two further peptide alterations not related to the temperature-sensitive phenotype: a C-terminal alteration in VP1 and an alteration unique to VP2. Cells infected by ts59 contain approximately fourfold lower amounts of viral capsid proteins and virus-specific messenger RNA at the restrictive temperature compared to the permissive temperature.
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