The synthesis rates of three proteins of tobacco mosaic virus (TMV), 160, 110, and 17.5 kDa, were monitored at intervals after interruption of synthesis of TMV RNA. Following inhibition of synthesis of both single-stranded and double-stranded RNAs by shifting wild type TMV to 40 degrees or ts mutant III2-35 to 35 degrees, the synthesis rates of viral proteins declined sequentially, with that of the larger proteins declining faster. When viral RNA synthesis was prevented with cordycepin, synthesis rates of the 110 and 160-kDa proteins declined rapidly, while the 17.5-kDa protein decreased more slowly. These data imply that the functional mRNA is transitory, probably nascent RNA, and that each protein is produced independently. The process of translation of viral mRNA was not temperature sensitive and occurred normally for brief periods after shift to restrictive temperatures. When single-stranded RNA synthesis was inhibited differentially from double-stranded RNA synthesis, protein synthesis was correlated with double-stranded RNA synthesis and not single-stranded RNA synthesis. Following a shift of ts mutant IV-35 to 35 degrees, a shift that immediately stopped single-stranded RNA synthesis without inhibiting double-stranded RNA synthesis, all three viral proteins continued to be produced normally. Also, after return of wild type TMV to 25 degrees after a 1-hr incubation at 40 degrees, viral protein and double-stranded RNA synthesis recovered in parallel to the normal rate after 8 hr whereas single-stranded RNA synthesis, which had been reduced more drastically, recovered more slowly after 16 hr.