7-Methylguanosine Modifications in tRNA

Abstract

More than 90 different modified nucleosides have been identified in tRNA. Among the tRNA modifications, the 7-methylguanosine (m7G) modification is found widely in eubacteria, eukaryotes, and a few archaea. In most cases, the m7G modification occurs at position 46 in the variable region and is a product of tRNA (m7G46) methyltransferase. The m7G46 modification forms a tertiary base pair with C13-G22, and stabilizes the tRNA structure. Recently, we have proposed a reaction mechanism for eubacterial tRNA m7G methyltransferase (TrmB) based on the results of biochemical studies and previous biochemical, bioinformatic, and structural studies by others. However, an experimentally determined mechanism of methyl-transfer remains to be ascertained. The physiological functions of m7G46 in tRNA have started to be determined over the past decade. To be able to better respond to diseases and infections in which the m7G modification is considered to be involved, it is still necessary to further understand the catalytic mechanism of AdoMet and/or the tRNA bound form of m7G methyltransferases. In this review, information of tRNA m7G modifications and tRNA m7G methyltransferases are summarized and the differences in reaction mechanism between tRNA m7G methyltransferase and rRNA or mRNA m7G methylation enzyme are discussed.