A novel species of double stranded RNA in mitochondria of Saccharomyces cerevisiae.

A double stranded RNA species has been detected in guanidine hydrochloride extracts of mitochondria from respiratory competent cells of Saccharomyces cerevisiae. This novel mitochondrial RNA, termed mtdsRNA, has been purified in a Cs2SO4 density gradient where it bands at a density of 1.58 g/ml. The mtdsRNA runs as a single slow moving band on agarose gels. Its double stranded RNA character was evidenced by its sensitivity to digestion by RNase III, but not by RNase H, or DNase I. Moreover the mtdsRNA hybridized to each separated strand of a petite mtDNA. It is concluded that mtdsRNA contains long transcripts derived from most regions of yeast mtDNA, because 1) its weight-average length as determined by electron microscopy was 4.5 micrometer (about 14 kb, or 20% of the wild type mtDNA genome), and 2) it hybridized to each of a series of eight petite mtDNA probes carrying sequences derived from widely different segments of mtDNA. It is proposed that prolonged transcription of both strands of yeast mtDNA can occur and that mtdsRNA arises from hybridization of these long complementary transcripts.