S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the C(5) position of cytosine 2870 (m5C2870) in 25S rRNA. Required for 60S ribosomal subunit synthesis and processing. cytidine(2870) in 25S rRNA + S-adenosyl-L-methionine = 5-methylcytidine(2870) in 25S rRNA + H(+) + S-adenosyl-L-homocysteine Interacts with NOP53. Interacts with TRM112. Present with 18700 molecules/cell in log phase SD medium. Belongs to the class I-like SAM-binding methyltransferase superfamily. RsmB/NOP family.