FUNCTION OF ROTAVIRUS VP3 POLYPEPTIDE IN VIRAL MORPHOGENESIS

The phenotype of the rotavirus SA-11 mutant tsB carrying a thermosensi tive mutation in gene 3, which encodes VP3, was characterized further from both infected cells and purified viral particles. The mutant phen otype was initially identified as negative for in vivo double- and sin gle-stranded RNA synthesis. Our results show that the in vitro transcr iptional properties of the tsB mutant at the restrictive temperature w ere identical to those of the wild-type strain. Similar results were o btained with respect to the VP3-associated guanylyl-transferase activi ty. Analysis of viral particles made by mutant-infected cells at the r estrictive temperature showed that only empty single-shelled particles were assembled. This indicates that viral morphogenesis is halted aft er the initial viral transcription and before RNA replication, suggest ing that VP3 may be required as part of the replicase system but not f or subviral particle assembly. These data suggest that such a phenotyp e is not due to alteration of a VP3 function related to transcription.