Conformation and template activity of human reovirus genome RNA

In vitro activation of human reovirus transcriptase by alpha-chymotrypsin digestion of viral outer shell proteins was completely dependent on the ionic size of the monovalent cation in the medium. Cations with nonhydrated ionic radii larger than 1.3 A showed full potency of activation of chymotrypsin digestion, and produced transcriptionally active virus cores. Smaller cations having ionic radii of 0.6 A or 0.95 A, on the other hand, promoted the chymotrypsin digestion to lesser extents, and yielded subviral particles showing latent or very low transcriptase activities. Differential conformational changes would be induced in viral outer shell proteins by these monovalent cations, resulting in the varied accessibility to chymotrypsin. Electron microscopic analyses under denaturing conditions of the cross-linked reovirus core genome RNAs with the AMT photoreaction revealed that they were almost evenly cross-linked by the psoralen adducts forming no reproducible size of "bubbles." This result suggests that the double helical reovirus genome may not be bound tightly by the inner viral proteins forming such nucleoprotein structures as nucleosomes in eukaryotic chromatin.