Properties of a discrete high molecular weight poly(A) containing mitochondrial RNA

Pulse-labeled mitochondrial RNA from hamster cells contains a number of discrete high molecular weight polyA(+)] and polyA(?)] RNAs. Characterization of the largest and most plentiful of the polyA(+)] RNAs, the “20S_E RNA,” showed it to be a labile, unmethylated component with a molecular weight ～- 730,000. Hybridization of the 20S_E RNA to mtDNA was 60–70% inhibited in the presence of excess 17S rRNA, suggesting a significant degree of primary sequence homology between these RNA species. In vitro treatment with RNAse III converted the 20S_E RNA to a polyA(?)] “17S” product, while similar treatment of mitochondrial 17S rRNA or a polyA(+)] 12S_E RNA had no effect on these RNAs. These data support the proposition that the 20S_E RNA is a precursor to the 17S rRNA.