Regulated, stable expression and nuclear presence of reovirus double-stranded RNA-binding protein sigma 3 in HeLa cells

Reovirus genome segment S4 codes for polypeptide sigma 3, a major outer capsid component of virions and a double-stranded RNA (dsRNA)-binding protein implicated in viral cytopathogenesis. We have constructed a stable HeLa cell line (S4tTA) that produces functional sigma 3 under tetracycline transactivator control, In the absence of tetracycline, S4tTA cells synthesized stable dsRNA-binding sigma 3 that accumulated in the nucleus as well as in the cytoplasm, However, in induced S4tTA cells also expressing reovirus outer shell polypeptide mu 1/mu 1C, migration of sigma 3 into the nucleus was blocked, probably as a result of formation of a complex with mu 1/mu 1C which was exclusively in the cytoplasm, Mutant analyses indicated a correlation between dsRNA-binding activity and nuclear entry of sigma 3, suggesting an additional role(s) for this capsid protein in virus-cell interactions.