7-methylguanosine modifications in transfer RNA (tRNA)

Abstract

More than 90 different modified nucleosides have been identified in tRNA. Among the tRNA modifications, the 7-methylguanosine (m 7 G) modification is found widely in eubacteria, eukaryotes, and a few archaea. In most cases, the m 7 G modification occurs at position 46 in the variable region and is a product of tRNA (m 7 G46) methyltransferase. The m 7 G46 modification forms a tertiary base pair with C13-G22, and stabilizes the tRNA structure. A reaction mechanism for eubacterial tRNA m 7 G methyltransferase has been proposed based on the results of biochemical, bioinformatic, and structural studies. However, an experimentally determined mechanism of methyl-transfer remains to be ascertained. The physiological functions of m 7 G46 in tRNA have started to be determined over the past decade. For example, tRNA m 7 G46 or tRNA (m 7 G46) methyltransferase controls the amount of other tRNA modifications in thermophilic bacteria, contributes to the pathogenic infectivity, and is also associated with several diseases. In this review, information of tRNA m 7 G modifications and tRNA m 7 G methyltransferases is summarized and the differences in reaction mechanism between tRNA m 7 G methyltransferase and rRNA or mRNA m 7 G methylation enzyme are discussed.