Encephalomyocarditis virus multiplication in the presence of pyronine.

Pyronine at non-toxic concentrations greatly reduced the yield of encephalomyocarditis virus produced by Krebs ascites cells. The inhibition was greatest when pyronine was added 2 hr after infection and was less when the dye was added later. It also decreased when the dye was added shortly before infection. It could be reversed by removing pyronine from infected cells less than 2 hr after treatment. In the presence of the dye, synthesis of virus RNA was inhibited; the residual singlestranded RNA synthesized was not infectious and had abnormal sedimentation characteristics. Infectious double-stranded virus RNA was synthesized normally for 3 hr after infection and was inhibited later. Both virus and cellular protein synthesis were inhibited by pyronine. A possible explanation for these results could be the modification of the template activity of double-stranded virus RNA due to intercalation of pyronine between the base pairs.