S-adenosyl-L-methionine-dependent methyltransferase that mediates N(3)-methylcytidine modification of residue 32 of the tRNA anticodon loop of tRNA(Ser), including tRNA(Ser)(UGA) and tRNA(Ser)(GCU) (PubMed:28655767). Interaction with SARS1/SerRS is required for N(3)-methylcytidine methylation (By similarity). cytidine(32) in tRNA(Ser) + S-adenosyl-L-methionine = H(+) + N(3)-methylcytidine(32) in tRNA(Ser) + S-adenosyl-L-homocysteine Monomer (By similarity). Interacts with SARS1/SerRS; interaction is mediated via tRNA(Ser) and is required for N(3)-methylcytidine methylation (By similarity). Mice were born with normal Mendelian ratio without developmental defects (PubMed:28655767, PubMed:32923617). However, male show a significant reduction in body weight over time due to reduced energy expenditure (PubMed:32923617). Cells show reduced N(3)-methylcytidine modification in tRNA fractions (PubMed:28655767). Due to intron retention. Belongs to the methyltransferase superfamily. METL family.