O-methyltransferase that specifically monomethylates 5'-monophosphate of cytoplasmic histidyl tRNA (tRNA(His，acting as a capping enzyme by protecting tRNA(His from cleavage by DICER1. Also able，with less efficiently，to methylate the 5' monophosphate of a subset of pre-miRNAs，acting as a negative regulator of miRNA processing. The 5' monophosphate of pre-miRNAs is recognized by DICER1 and is required for pre-miRNAs processing: methylation at this position reduces the processing of pre-miRNAs by DICER1. Was also reported to mediate dimethylation of pre-miR-145; however dimethylation cannot be reproduced by another group which observes a monomethylation of pre-miR-145.