Small reovirus-specific particle with polycytidylate-dependent RNA polymerase activity

Abstract

It was previously reported that virus-specific particles with [poly(C)]-dependent RNA polymerase activity accumulated at 30.degree. C in reovirus-infected cells. These particles sedimented heterogeneously from 300-550S and traversed through a 40% glycerol cushion to the pellet in 3 h at 190,000 .times. g. This study showed that smaller particles with poly(C)-dependent RNA polymerase activity remained in the glycerol cushion. These smaller, enzymatically active particles, when purified, sedimented at 15-16S. They were spherical or triangular with a diameter of 11-12 nm. They were comprised mostly, and likely solely, of 1 reovirus protein, sigma NS. No particles with poly(C)-dependent RNA polymerase activity were found in mock-infected [mouse fibroblast L] cells. Chromatography on the cation exchanger, CM-Sephadex, ascertained that sigma NS was the poly(C)-dependent RNA polymerase and showed its existence in 2 forms. In one form, it was enzymatically active and eluted from the column at 0.5 M KCl. In the enzymatically inactive state, it did not bind to the column. The enzymatically active form of sigma NS carries a greater net positive charge than the inactive form. They also suggest that both forms of sigma NS are associated with a particle which has poly(C)-dependent RNA polymerase activity.