CHARACTERIZATION OF THE THERMOSENSITIVE TS453 REOVIRUS MUTANT - INCREASED DSRNA BINDING OF SIGMA-3 PROTEIN CORRELATES WITH INTERFERON RESISTANCE

The mutation harbored by the reovirus ts453 thermosensitive mutant has been assigned to the S4 gene encoding the major outer capsid protein sigma 3. Previous gene sequencing has identified a nonconservative ami no acid substitution located near the zinc finger of sigma 3 protein i n the mutant. Coexpression in COS cells of the sigma 3 protein present ing this amino acid substitution (N16K), together with the other major capsid protein mu 1, has also revealed an altered interaction between the two proteins; this altered interaction prevents the sigma 3-depen dent cleavage of mu 1 to mu 1C. This could explain the lack of outer c apsid assembly observed during ts453 virus infection at nonpermissive temperature. In the present study, we pursued the characterization of this mutant sigma 3 protein. Although the N16K mutation is located clo se to the zinc finger region, it did not affect the ability of the pro tein to bind zinc. In contrast, this mutation, as well as mutations wi thin the zinc finger motif itself, can increase the binding of the pro tein to double-stranded RNA(dsRNA). II also appears that the N16K muta nt protein is more efficiently transported to the nucleus than the wil d-type protein, an observation consistent with the postulated role of dsRNA binding in sigma 3 nuclear presence. The lack of association wit h sigma 1, and/or the increased dsRNA-binding activity of sigma 3, cou ld be responsible for a partial resistance of the ts453 virus to inter feron treatment and this could have important consequences in the cont ext of protein synthesis regulation during natural reovirus infection. (C) 1998 Academic Press.