Putative chicken “muscle-specific 7 S RNA” is related to the mitochondrial ATPase 6 gene

Sequence analysis of the mitochondrial ATPase 6 gene from chicken revealed that its 3′ region is virtually identical with a chicken muscle-specific 7 S RNA which was reported to induce the expression of tissue-specific functions in blastoderm explants. Using chicken and quail cell lines depleted of mitochondrial DNA, we demonstrate that the 7 S RNA is encoded by the mitochondrial genome and not by nuclear (repetitive) DNA as suggested previously. Moreover, no 7 S RNA-homologous transcript of the expected length (about 400 bases) is detected, either in these cell lines or in heart and liver tissues. The only RNA species hybridizing with a 7 S RNA-specific probe is an abundant, 900 base long transcript of mitochondrial origin that we identify as the ATPase 8-ATPase 6 fused messenger. We suggest that the characterized muscle-specific 7 S RNA cDNA is derived from an unrelated contaminant in the blastoderm-inducing fraction.