The function of NOP2 (NOP2 nucleolar protein, ENSG00000111641) is as follows. S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the C(5) position of cytosine 4447 in 28S rRNA (PubMed:26196125). Required for efficient rRNA processing and 60S ribosomal subunit biogenesis (PubMed:24120868, PubMed:36161484). Regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNAs and facilitates the recruitment of U3 and U8 snoRNAs to pre-90S ribosomal particles and their stable assembly into snoRNP complexes (PubMed:36161484). May play a role in the regulation of the cell cycle and the increased nucleolar activity that is associated with the cell proliferation (PubMed:24120868). {ECO:0000269|PubMed:24120868, ECO:0000269|PubMed:26196125, ECO:0000269|PubMed:36161484}.