Protein-histidine N-methyltransferase that specifically catalyzes the N1-methylation (pros-methylation) of histidine residues in a wide range of proteins. It primarily monomethylates proteins containing RNA-binding C3H1 zinc finger motifs, such as U2AF1, ZC3H15, ZC3H18, PPP1R10, PRR3 and RNF113A, thereby modulating mRNA splicing and turnover (PubMed:37612136, PubMed:39198440, PubMed:40473212). Additionally, methylates the dipeptide carnosine (beta-alanyl-L- histidine) at the N1 position to generate anserine, an abundant component of vertebrate skeletal muscle. Acts also on other L- histidine-containing di- and tripeptides, such as Gly-Gly-His, Gly-His, and homocarnosine (GABA-His) (PubMed:26001783). {ECO:0000269|PubMed:26001783, ECO:0000269|PubMed:37612136, ECO:0000269|PubMed:39198440, ECO:0000269|PubMed:40473212}. This is the function of CARNMT1 (carnosine N-methyltransferase 1, Ensembl gene identifier ENSG00000156017).