Saccharomyces cerevisiae Eukaryotic Elongation Factor 1A (eEF1A) Is Methylated at Lys-390 by a METTL21-Like Methyltransferase.
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YNL024C/EFM6 is required for methylation of eEF1A at Lys390; the residue is monomethylated in wild-type cells but exclusively unmethylated in a ynl024c deletion strain, establishing EFM6 as the responsible methyltransferase.
"we here show that the YNL024C gene is required for methylation of eEF1A at Lys390, the only of these methylations for which the responsible MTase has not yet been identified."
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Overexpression of EFM6 dramatically increases eEF1A-Lys390 methylation, with trimethylation becoming predominant, demonstrating that EFM6 activity drives the modification.
"over-expression of Ynl024c caused a dramatic increase in Lys390 methylation, with trimethylation becoming the predominant state."
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EFM6 directly methylates eEF1A in vitro (GTP-dependent labelling of the ~50 kDa eEF1A band by an E. coli extract expressing EFM6), indicating a direct methyltransferase activity on eEF1A rather than an indirect effect.
"when GTP was present, a markedly stronger, Ynl024c-specific labelling was observed in the 50 kDa region of the ynl024cΔ yeast extract"
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EFM6 is highly specific for eEF1A and, unlike its closest human homolog METTL21A, does not methylate yeast Hsp70 proteins.
"demonstrating that the enzyme is highly specific for eEF1A"
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EFM6 harbours the conserved seven-beta-strand methyltransferase motifs (Motif I, Motif post I, Motif II) and the MTF16 hallmark DXXY motif, confirming it as a Class I SAM-dependent methyltransferase.
"Ynl024c harbours hallmark conserved motifs found in 7BS MTases, i. e. Motif I, Motif post I and Motif II"
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The biological significance of EFM6-mediated eEF1A-Lys390 methylation is unknown and remains to be determined.
"the precise function of Efm6-mediated eEF1A methylation does remain an enigma and further studies are required to reveal its role."