Co-ordinate control of gene expression. Muscle-specific 7 S RNA contains sequences homologous to 3'-untranslated regions of myosin genes and repetitive DNA.

We have cloned and sequenced a complementary DNA copy (pSS48) of a novel muscle-specific, low molecular weight RNA, 7 S RNA, isolated from embryonic chick cardiac muscle cells. The hybridization pattern of plasmid pSS48 DNA to chick genomic DNA suggests that 7 S RNA is derived from the repetitive chick DNA with a repetition frequency of about 300 copies per haploid genome. Under low stringency, pSS48 DNA also hybridizes with high specificity to the single copy gene for chick myosin light chain (MLC) and to myosin heavy chain (MHC), and possibly to other co-ordinately expressed genes for chick muscle proteins. The sequence analysis of recombinant plasmids pSS48, pML10 and pMHC8, for 7 S RNA, MLC mRNA and MHC RNA, respectively, indicated that short nucleotide stretches homologous to 7 S RNA reside in the 3' untranslated regions of the respective genes. The 7 S RNA sequence appears to be highly specific for the chick muscle tissue, since RNA and DNA from several sources did not hybridize to pSS48 DNA. Furthermore, the 7 S RNA-like sequence(s) appears in chick blastodermal cells preferentially earlier than the onset of transcription of genes for major muscle proteins. These results, taken together, suggest a possible function for 7 S RNA in expression of muscle-specific genes during chick development.