PREFERENTIAL TRANSLATION OF REOVIRUS MESSENGER-RNA BY A SIGMA-3-DEPENDENT MECHANISM

We have characterized reovirus strains that differ in the degree to wh ich they inhibit cellular protein synthesis and used them to investiga te mechanisms regulating gene expression in infected cells. A previous genetic study associated distinct effects of reovirus strains on cell ular translation with polymorphisms in viral protein as. In cell extra cts, as sequesters double-stranded RNA (dsRNA) and blocks activation o f the dsRNA-activated protein kinase (PKR), an interferon-Induced enzy me that inhibits translational initiation by phosphorylating elF-2 alp ha. We found that in Infected cells, cellular protein synthesis is tra nslationally regulated in a strain-specific manner. Using immunoprecip itation and indirect immunofluorescence we showed that the effect of a strain on cellular translation is not determined by the level of sigm a 3, but appears to result from differences in sigma 3 localization. I n cells infected with a strain that spares cellular translation, sigma 3 is present throughout the cytoplasm, whereas in cells infected with inhibitory strains, sigma 3 is restricted to perinuclear viral factor ies. Biochemical studies suggested that diffuse localization of sigma 3 is a consequence of low affinity for capsid protein mu 1. Our findin gs are consistent with a model in which the efficiency of cellular tra nslation is determined by the cytoplasmic level of sigma 3 that is not complexed with mu 1. (C) 1997 Academic Press.