Formation of m2G6 in Methanocaldococcus jannaschii tRNA catalyzed by the novel methyltransferase Trm14
The modified nucleosides N2-methylguanosine and N22-dimethylguanosine in transfer RNA occur at five positions in the D and anticodon arms, and at positions G6 and G7 in the acceptor stem. Trm1 and Trm11 enzymes are known to be responsible for several of the D/anticodon arm modifications, but methylases catalyzing post-transcriptional m2G synthesis in the acceptor stem are uncharacterized. Here, we report that the MJ0438 gene from Methanocaldococcus jannaschii encodes a novel S-adenosylmethionine-dependent methyltransferase, now identified as Trm14, which generates m2G at position 6 in tRNACys. The 381 amino acid Trm14 protein possesses a canonical RNA recognition THUMP domain at the amino terminus, followed by a γ-class Rossmann fold amino-methyltransferase catalytic domain featuring the signature NPPY active site motif. Trm14 is associated with cluster of orthologous groups (COG) 0116, and most closely resembles the m2G10 tRNA methylase Trm11. Phylogenetic analysis reveals a canonical archaeal/bacterial evolutionary separation with 20–30% sequence identities between the two branches, but it is likely that the detailed functions of COG 0116 enzymes differ between the archaeal and bacterial domains. In the archaeal branch, the protein is found exclusively in thermophiles. More distantly related Trm14 homologs were also identified in eukaryotes known to possess the m2G6 tRNA modification.
[…] Initial comparative analysis of a limited subset of methanogen genomes was performed using STRING (v 6.2) (). Sequence homology searches to the omniome or selected subsets of the omniome were performed with BLAST (). For phylogenetic analysis, the multiple sequence alignment for a subset of proteins within COG 0116 was carried out using ClustalW (). The phylogenetic tree based on these sequences was constructed with MEGA5 (), using the neighbor-joining method with the BioNJ(JTT) model. The bootstrap test (1000 replicates) was performed to validate the stability of the nodes. […]
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