Chemical and physical properties of mammalian mitochondrial aminoacyl-transfer RNAs. II. Analysis of 7-methylguanosine in mitochondrial and cytosolic aminoacyl-transfer RNAs.

The 7-methylguanosine (m7G) content of two individual mitochondrial tRNAs, labelled in the aminoacyl moiety was assayed by the specific cleavage of the tRNA at this nucleotide followed by electrophoretic analysis to identify the 3'-terminal fragment of the tRNA. Neither Syriam hamster mitochondrial tRNALeu nor tRNAMet were found to contain m7G. In contrast, cytosolic tRNAMetS were cleaved indicating the presence of m7G, apparently 27--28 and 29 nucleotides from their 3' terminus. Cystolic tRNALeu was not cleaved. These results are discussed in relationship to the reported low content of methylated nucleosides in mitochondrial 4 S RNA.