Trmt61B is a methyltransferase responsible for 1-methyladenosine at position 58 of human mitochondrial tRNAs

Abstract

In human mitochondria, 1-methyladenosine (m1A) occurs at position 58 of tRNALeu(UUR). In addition, partial m1A58 modifications have been found in human mitochondrial tRNALys and tRNASer(UCN). We identified human Trmt61B, which encodes a mitochondria-specific tRNA methyltransferase responsible for m1A58 in these three tRNAs. Trmt61B is dominantly localized to the mitochondria. m1A58 formation in human mitochondrial tRNALeu(UUR) could be reconstituted in vitro using recombinant Trmt61B in the presence of Ado-Met as a methyl donor. Unlike the cytoplasmic tRNA m1A58 methyltransferase that consists of an α2β2 heterotetramer formed by Trmt61A and Trmt6, Trmt61B formed a homo-oligomer (presumably a homotetramer) that resembled the bacterial homotetrameric m1A58 methyltransferase. The bacterial origin of Trmt61B is supported by the results of the phylogenetic analysis.