Function
O-methyltransferase that specifically monomethylates 5'-monophosphate of cytoplasmic histidyl tRNA, acting as a capping enzyme (PubMed:28119416). Less efficiently, also methylates the 5' monophosphate of pre-miRNAs, acting as a negative regulator of miRNA processing (PubMed:23063121, PubMed:28119416). 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. Able to mediate methylation of pre-miR-145, as well as other pre-miRNAs (PubMed:23063121). There is some controversy about the methylation of pre-miR-145, since the dimethylation first described as the specific enzymatic activity cannot be reproduced by a more recent work which observes a monomehtylation of pre-miR-145 but two orders weaker than the methylation of cytosolic histidyl tRNA (PubMed:23063121, PubMed:28119416, PubMed:30127802).