Required Elements in tRNA for Methylation by the Eukaryotic tRNA (Guanine-N(2)-) Methyltransferase (Trm11-Trm112 Complex)

The Saccharomyces cerevisiae Trm11 and Trm112 complex (Trm11-Trm112) methylates the 2-amino group of guanosine at position 10 in tRNA and forms N(2)-methylguanosine. To determine the elements required in tRNA for methylation by Trm11-Trm112, we prepared 60 tRNA transcript variants and tested them for methylation by Trm11-Trm112. The results show that the precursor tRNA is not a substrate for Trm11-Trm112. Furthermore, the CCA terminus is essential for methylation by Trm11-Trm112, and Trm11-Trm112 also only methylates tRNAs with a regular-size variable region. In addition, the G10-C25 base pair is required for methylation by Trm11-Trm112. The data also demonstrated that Trm11-Trm112 recognizes the anticodon-loop and that U38 in tRNA(Ala) acts negatively in terms of methylation. Likewise, the U32-A38 base pair in tRNA(Cys) negatively affects methylation. The only exception in our in vitro study was tRNA(Val)(AAC1). Our experiments showed that the tRNA(Val)(AAC1) transcript was slowly methylated by Trm11-Trm112. However, position 10 in this tRNA was reported to be unmodified G. We purified tRNA(Val)(AAC1) from wild-type and trm11 gene deletion strains and confirmed that a portion of tRNA(Val)(AAC1) is methylated by Trm11-Trm112 in S. cerevisiae. Thus, our study explains the m(2)G10 modification pattern of all S. cerevisiae class I tRNAs and elucidates the Trm11-Trm112 binding sites.