The function of FBLL1 (fibrillarin like rRNA 2'-O-methyltransferase 1, Ensembl gene identifier ENSG00000188573) is as follows. S-adenosyl-L-methionine-dependent RNA methyltransferase that catalyzes 2'-hydroxyl ribose methylation in RNAs (PubMed:39570315). Functions as part of box C/D small nucleolar ribonucleoprotein (snoRNP) complexes, where guide snoRNAs ensure methylation specificity through base pairing with RNA substrates (PubMed:39570315). Exhibits broad substrate specificity, methylating multiple sites on ribosomal RNAs (rRNAs) and messenger RNAs (mRNAs) depending on the guide snoRNA incorporated in the complex (PubMed:39570315). Specifically expressed in brain, it regulates the expression of GAP43 by stabilizing its mRNA through methylation and thereby plays an indirect role in neuronal differentiation (By similarity). {ECO:0000250|UniProtKB:Q80WS3, ECO:0000269|PubMed:39570315}.