Nucleotide sequences (sarc) related to the transforming gene of avian sarcoma viruses are present in the DNA and transcribed into RNA in uninfected avian cells (Stehelin et al., 1976b; Spector et al., 1978). Cytoplasmic RNA containing the sarc sequences has a sedimentation coefficient of 30S, is linked to polyadenylic acid and is present in polyribosomes in a form which can be released by treatment with EDTA. Hence the sarc sequences (complexity = 5 x 10(5) daltons) are part of a larger transcriptional unit (approximately 1.8 x 10(6) daltons), and the sarc RNA appears to serve an as yet unknown messenger function. In addition, the sarc sequences in chicken cells are not linked to RNA transcribed from the provisrus of the endogenous virus RAV-O, since RAV-O cytoplasmic RNA has sedimentation coefficients of 32S and 21S. Comparison of sarc-containing RNA in quail embryo fibroblasts and in quail cells derived from a methylcholanthrene-induced fibrosarcoma revealed no differences with respect to size, polyadenylation or concentration of the RNA in nuclei, cytoplasm and polyribosomes; thus the phenotypic differences between these cells are unlikely to be a consequence of alteration in expression of the sarc sequences.