Methylation properties of mitochondrion—Specific transfer RNA from cultured hamster cells

The degree of methylation and methylated nucleotide content of hamster-cell mitochondrial tRNA has been examined separately from the cytoplasmic RNA that purifies with mitochondria, via a combination of multipleisotope experiments, preferential inhibition of mitochondrial RNA synthesis by ethidium bromide, and gel electrophoresis under conditions that partially resolve mitochondrial and cytoplasmic tRNA. Mitochondrial tRNA was found to be 32% as heavily methylated as cytoplasmic tRNA and to be deficient in methylated pyrimidine and ribose components present in cytoplasmic tRNA. Both tRNA types contained 1-methyladenine as the sole methylated adenine, but the methylated guanine patterns of the two types differed substantially. Possible evolutionary implications of these findings have been discussed.