Emerging Insights into the Moonlighting Functions and Evolutionary Origins of Mitochondrial RNA Methyltransferases

Abstract

Mitochondria; RNA Methyltransferase; Pentatricopeptide repeat; Mitochondrial transcription factorRNA methyltransferases mediate the addition of methyl groups to ribonucleotides. Such modifications have implications for the structure and function of RNA. While methylation is reported in mitochondrial RNAs, the enzymes that catalyze these reactions often remain elusive; however with advances in sequencing technologies, genomic analysis is beginning to uncover their identities. Due to the complex evolutionary history of mitochondria, little is known about the origin and function of methyltransferases. This article explores two emerging families of mitochondrial RNA methyltransferases. We discuss the evidence suggesting they possess diverse bacterial (endosymbiotic and non-endosymbiotic) origins and have acquired functions in addition to methylation.The mitochondrial transcription factor B (mtTFB) proteins function in transcription initiation by associating with the other components of the mitochondrial transcription machinery to induce open-complex formation [1]. They also mediate the methylation of mitochondrial small subunit rRNA to facilitate ribosome assembly, stability and biogenesis [2]. The mtTFB proteins are widespread throughout eukaryotes and have arisen from a bacterial dimethyltransferase (DMT) family, which subsequently obtained a secondary function as a transcription factor. The homology between mtTFB and an