Identification and Characterization of a Double-Stranded RNA Reovirus Temperature-Sensitive Mutant Defective in Minor Core Protein m2

A newly identified temperature-sensitive mutant whose defect was mapped to the reovirus M1 gene (minor core protein m2) was studied to better understand the functions of this virion protein. Sequence determination of the M1 gene of this mutant (tsH11.2) revealed a predicted methionine-to-threonine alteration at amino acid 399 and a change from proline to histidine at amino acid 414. The mutant made normal amounts of single-stranded RNA, both in in vitro transcriptase assays and in infected cells, and normal amounts of progeny viral protein at early times in a restrictive infection. However, tsH11.2 produced neither detectable progeny protein nor double-stranded RNA at late times in a restrictive infection. These studies indicate that m2 plays a role in the conversion of reovirus mRNA to progeny double-stranded RNA.