SV40 LARGE T-ANTIGEN FUNCTIONS AT 2 DISTINCT STEPS IN VIRION ASSEMBLY

The SV40 large T antigen mutant 5002 has two amino acid substitutions (L19-F; P28-S) and is defective for productive viral infection as demo nstrated by its small plaques that arise very late and by a 100-fold r educed yield of infectious progeny. 5002 replicates viral DNA at the s ame time postinfection as wild-type SV40, and the production of progen y DNA molecules is only marginally reduced, Furthermore, the viral cap sid proteins accumulate to near normal levels following infection with 5002. In this manuscript we report evidence that 5002 infection is bl ocked at a specific stage of viral assembly. The SV40 viral assembly p athway involves conversion of 75S chromatin complexes to 240S virions. Unlike mutants within the T antigen host range (HR) domain, that are also defective for viral assembly and accumulate 75S particles (Spence and Pipas, 1994), 5002 particles are blocked as 150S previrions conta ining viral DNA and capsid proteins. We have previously shown that 500 2 and HR mutants cooperate to produce viable progeny in trans compleme ntation tests. Thus, by two criteria, SV40 large T antigen encodes two distinct activities that function at different steps in virion assemb ly. (C) 1994 Academic Press, Inc.