CMTr mediated 2`-O-ribose methylation status of cap adjacent-nucleotides across animals

Cap methyltransferases (CMTrs) O-methylate the 2` position of the ribose (cOMe) of cap-adjacent nucleotides of animal, protist and viral mRNAs. Animals generally have two CMTrs, while trypanosomes have three and many viruses encode one in their genome. In the splice leader of mRNAs in trypanosomes the first four nucleotides contain cOMe, but little is known about the status of cOMe in animals. Here, we show that cOMe is prominently present on the first two cap-adjacent nucleotides with species- and tissue-specific variations in C. elegans, honeybees, zebrafish, mouse and human cell lines. In contrast, Drosophila contains cOMe primarly on the first cap-adjacent nucleotide. De novo RoseTTA modelling of CMTrs reveals close similarities of the overall structure and near identity for the catalytic tetrad, and for cap and co-factor binding for human, Drosophila and C. elegans CMTrs. While viral CMTrs maintain the overall structure and catalytic tetrad, they have diverged in cap and co-factor binding. Consistent with the structural similarity, both CMTrs from Drosophila and humans methylate the first cap-adjacent nucleotide of an AGU consensus start. Since the second nucleotide is also methylated upon heat stress in Drosophila, these findings argue for regulated cOMe important for gene expression regulation.