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