Caenorhabditis elegans ZC376.5 encodes a tRNA(m super(2) sub(2)G sub(26))dimethyltransferase in which super(246)arginine is important for the enzyme activity

It has been estimated that eukaryotes carry more than 50 genes for tRNA modifying enzymes. Of the few so far identified most come from yeast, a lower eukaryote. In Saccharomyces cerevisiae, the TRM1 gene is a nuclear gene encoding the tRNA(m super(2) sub(2)G sub(26))dimethyltransferase, which catalyses the formation of the N super(2), N super(2)-dimethylguanosine at position 26 in tRNA. We have isolated and characterized the corresponding gene ZC376.5 in Caenorhabditis elegans. Via RT-PCR the cDNA sequence of the full length ZC376.5 has now been cloned, expressed in Escherichia coli and demonstrated to encode a tRNA(m super(2) sub(2)G sub(26))dimethyltransferase that produces dimethyl-G sub(26) in vivo and in vitro with tRNA from yeast and bacteria as substrates. This is the first example of a complete gene sequence coding for a tRNA modifying enzyme from a multicellular organism. A point mutation in exon IV in the C. elegans genome sequence coding for the tRNA(m super(2) sub(2)G sub(26))methyltransferase that substituted arginine246 for glycine eliminated the modification activity. Exchanging the corresponding lysine residue in the yeast Trm1p for alanine caused a severe loss of activity, indicating that the identity of the amino acid at this position is important for enzyme activity.