SUMMARYNucleoprotein preparations of tobacco rattle virus (TRV) strain SYM contain particles of four modal lengths. Particles of length 188 nm and 101 nm contain RNA-1 and RNA-2 respectively. Those of length 57 nm and 48 nm contain RNA molecules that are not required for infectivity but include specific sequences derived from both RNA-I and RNA-2. No products attributable to translation of RNA-2 were obtained in reticulocyte lysates, whereas RNA-2 of other TRV strains serves as messenger RNA for virus coat protein, In strain SYM, one of the smaller RNA species, RNA-3 (mol. wt. 0.6 x 106, 1750 nucleotides), was translated in vitro to give coat protein, and is apparently a subgenomic messenger RNA derived from RNA-2. The other small RNA species, RNA-4 (mol. wt. 0-54 × 106, 1550 nucleotides), was translated into a polypeptide of apparent mol. wt. 29000, unrelated to coat protein. It is suggested that RNA-4 is a subgenomic messenger RNA derived from RNA-1.