Methylated nucleotide content of mitochondrial ribosomal RNA from hamster cells

We have examined the state of methylation of mitochondrial ribosomal RNA from cultured hamster (BHK-21) cells. Ethidium-sensitive, and hence mitochondrion-specific, methylation levels were determined using multiple isotope techniques and improved purification procedures. The larger mitochondrial rRNA species, 17 S RNA, was found to contain 0.13 methyl group per 100 nucleotides and the smaller, 13 S RNA, 0.37. Methylated nucleotide and base analysis indicated that 17 S RNA contained one ribose-methylated residue (UmUp) per molecule and one unidentified residue; and 13 S RNA contained one methylated cytosine residue, one N⁶-dimethyladenine residue and one thymine residue per molecule. Possible evolutionary implications of these findings have been discussed.