Involved in ribosomal large subunit assembly (PubMed:24120868). S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the C(5) position of cytosine 4447 in 28S rRNA (Probable). May play a role in the regulation of the cell cycle and the increased nucleolar activity that is associated with the cell proliferation (Probable). cytidine(4447) in 28S rRNA + S-adenosyl-L-methionine = 5-methylcytidine(4447) in 28S rRNA + H(+) + S-adenosyl-L-homocysteine Interacts with MCRS1 (PubMed:9654073). Interacts with WDR46 (PubMed:23848194). Interacts with RRP1B (PubMed:20926688). Expressed in G1 and peaks during the early S phase of the cell cycle. Citrullinated by PADI4. Belongs to the class I-like SAM-binding methyltransferase superfamily. RsmB/NOP family.