Messenger Properties of TYMV-RNA

Abstract

Turnip yellow mosaic virus (TYMV) RNA extracted from virions (“virion” TYMV-RNA) contains two types of molecules of molecular weight 2 × 10 6: one which resists heat denaturation (“intact” TYMV-RNA) and one which yields smaller fragments upon heat denaturation (TYMV-RNA containing hidden breaks). A small RNA molecule of 0.2 × 10 6 MW is also present in virions. “Virion” TYMV-RNA can therefore be separated into “intact” RNA and smaller molecules by heat denaturation followed by sucrose gradient centrifugation. The RNA from the sucrose gradient fractions were analyzed by formamide PAGE: The small RNA with a molecular weight of 0.2 × 10 6 was separated from “intact” TYMV-RNA. The amount of coat protein synthesized by the RNA fractions when added to the wheat germ cell-free system was quite proportional to the amount of small RNA present. We conclude that coat protein synthesis is not directed by “intact” TYMV-RNA but by the small RNA. In addition, infectivity studies show that “intact” TYMV-RNA is fully infectious and thus it also contains the coat protein cistron.