A Messenger RNA for Tobacco Mosaic Virus Coat Protein in Infected Tobacco Mesophyll Protoplasts

Synthesis of tobacco mosaic virus (TMV)-specific low molecular weight component RNA (LMC) was investigated in relation to that of other TMV-related RNAs and proteins, and formation of progeny virus particles using synchronously infected tobacco mesophyll protoplasts. Timing of LMC synthesis was shown to be almost the same as, but somewhat earlier than that of TMV-RNA synthesis. In contrast, synthesis of TMV-specific double-stranded RNAs (replicative intermediate, RI and replicative form, RF) as well as a high molecular weight virus-induced protein (140 K protein) showed the maximum incorporation rate 4–6 h earlier than LMC synthesis. While, synthesis of coat protein and formation of progeny virus particles lagged behind LMC synthesis for 6–8 h. LMC occurring in polysomes was also investigated during the course of virus replication. The amount of produced coat protein calculated theoretically from the amount of LMC in polysomes of infected protoplasts was shown to be well agreed with the experimental results, indicating that LMC in polysomes is actively functioning as messenger for coat protien synthesis in vivo.