Activation of reovirion-associated poly(A) polymerase and oligomer methylase by cofactor-dependent cleavage of μ polypeptides

The factors influencing activation of the reovirion-associated enzymes which synthesize or modify reovirus oligonucleotides in vitro were studied. These are the poly(A) synthetase (Stoltzfus et al. 1974), and several methyltransferases (Carter 1977 1978). In the presence of chymotrypsin, enzyme activity appeared to be associated with particles possessing fragments of μ polypeptides of molecular weight ≈60,000 and 64,000. Reaction conditions which promoted generation of these polypeptides and oligomer-modifying or synthesizing activities failed to promote synthesis of complete transcripts of the viral genome. Conversion of subviral particles possessing the proteins associated with oligomer-dependent enzyme activity occurred only in reaction mixtures containing nucleoside triphosphates and an ATP-generating system in addition to chymotrypsin and Mn²⁺. This observation suggested that conversion might be dependent on the presence of nucleoside triphosphate in reaction mixtures. All of the products of nucleoside triphosphate hydrolysis exhibited a specific effect on μ cleavage and resulted in generation of particles which demonstrated either oligomer-dependent enzyme activities or transcriptase. These observations support the hypothesis that the pathway of uncoating may be modulated by cofactors of the virion-associated enzymes, resulting in activation of a specific subset of virion-associated activities.