The satellite cucumber mosaic virus (CMV)-associated RNA 5 (CARNA 5) of CMV strain S (CMV-S) which previously had been assigned the capability both to direct the synthesis of two small proteins in vitro (R. A. Owens and J. M. Kaper, 1977, Virology, 80, 196-203) and to induce the tomato necrosis disease in the presence of its helper virus (J. M. Kaper and H. E. Waterworth, 1977, Science, 196, 429-431), has been reinvestigated. Polyacrylamide gel electrophoretic analyses under partially denaturing conditions of CARNA 5 preparations from CMV-S grown in tobacco reveal a mixture of three distinct RNA species which have been isolated and partially characterized. In order of decreasing electrophoretic mobility they have been designated RNA 5, (n)CARNA 5, and (S)CARNA 5, respectively. RNA 5 has been partially sequenced and shown to represent 3'-terminal fragments of the CMV genomic RNAs. (n)CARNA 5 is responsible for the tomato necrosis-inducing properties of the mixture and coelectrophoreses with tomato necrosis-inducing CARNA 5 from CMV strain D. (S)CARNA 5 does not cause tomato necrosis; its complete nucleotide sequence was determined and is compared here to the published sequences of the CARNA 5s of four other CMV strains. A companion paper (M. J. Avila-Rincon et al., 1986, Virology, 152, 455-458) provides unequivocal evidence that the in vitro translation of nonnecrotic (S)CARNA 5 produces two small polypeptides resembling those described earlier.