Effects of Salts on RNA Polymerase Activity and Conformation of Filamentous Nucleoproteins of Rice Stripe Virus

Abstract

The RNA Polymerase associated with filamentous nucleoproteins of rice stripe virus (RSV) was irreversibly inactivated, when incubated in high concentrations of salts such as NaCl, KCl, CsCl, and NH₄Cl. In contrast, (NH₄)₂SO₄, Na₂SO₄, and Cs₂SO₄ did not affect the polymerase activity. In the standard assay mixture in which salts were incorporated, the SO₄^2- salts were more inhibitory to RNA polymerase activity than the Cl^- salts. With increasing concentrations of these salts, the fine, partially unfolded filamentous particles of RSV became more tightly coiled into stiff and rigid rods or apparently supercoiled circular filamentous particles. No distinct difference in structures of folded RSV particles was observed between Cl^- and SO₄^2- salts. The circular dichroism (CD) spectrum of RSV preparations in either the presence or absence of salts was that of a typical α helix. These observations indicate the tight folding of RSV particles in response to salts could be caused by tight stacking of the protein subunits in filamentous particles of RSV. The inhibitory effect of salts on the RNA polymerase activity is discussed.