RNA cytosine C(5)-methyltransferase that methylates cytosine to 5-methylcytosine (m5C) in various RNAs, such as tRNAs, mRNAs and some long non-coding RNAs (lncRNAs) (PubMed:22144916, PubMed:23871666, PubMed:31199786). Involved in various processes, such as epidermal stem cell differentiation, testis differentiation and maternal to zygotic transition during early development: acts by increasing protein synthesis; cytosine C(5)-methylation promoting tRNA stability and preventing mRNA decay (PubMed:22144916, PubMed:22885326, PubMed:23401851, PubMed:31199786). Methylates cytosine to 5-methylcytosine (m5C) at positions 34 and 48 of intron-containing tRNA(Leu)(CAA) precursors, and at positions 48, 49 and 50 of tRNA(Gly)(GCC) precursors (PubMed:22885326, PubMed:23871666, PubMed:31199786). tRNA methylation is required generation of RNA fragments derived from tRNAs (tRFs) (PubMed:31199786). Also mediates C(5)-methylation of mitochondrial tRNAs (PubMed:31276587, PubMed:31287866). Catalyzes cytosine C(5)-methylation of mRNAs, leading to stabilize them and prevent mRNA decay: mRNA stabilization involves YBX1 that specifically recognizes and binds m5C-modified transcripts (By similarity). Cytosine C(5)-methylation of mRNAs also regulates mRNA export: methylated transcripts are specifically recognized by THOC4/ALYREF, which mediates mRNA nucleo-cytoplasmic shuttling (By similarity). Also mediates cytosine C(5)-methylation of non-coding RNAs, such as vault RNAs (vtRNAs), promoting their processing into regulatory small RNAs (PubMed:23871666). Cytosine C(5)-methylation of vtRNA VTRNA1.1 promotes its processing into small-vault RNA4 (svRNA4) and regulates epidermal differentiation (By similarity). May act downstream of Myc to regulate epidermal cell growth and proliferation (PubMed:16713953). Required for proper spindle assembly and chromosome segregation, independently of its methyltransferase activity (PubMed:19596847). cytidine(48) in tRNA + S-adenosyl-L-methionine = 5-methylcytidine(48) in tRNA + H(+) + S-adenosyl-L-homocysteine cytidine(49) in tRNA + S-adenosyl-L-methionine = 5-methylcytidine(49) in tRNA + H(+) + S-adenosyl-L-homocysteine cytidine(50) in tRNA + S-adenosyl-L-methionine = 5-methylcytidine(50) in tRNA + H(+) + S-adenosyl-L-homocysteine cytidine(34) in tRNA precursor + S-adenosyl-L-methionine = 5-methylcytidine(34) in tRNA precursor + H(+) + S-adenosyl-L-homocysteine a cytidine in mRNA + S-adenosyl-L-methionine = a 5-methylcytidine in mRNA + H(+) + S-adenosyl-L-homocysteine Inhibited by magnesium ions. Interacts with NPM1 and NCL during interphase; interaction is disrupted following phosphorylation at Ser-139. Concentrated in the nucleolus during interphase and translocates to the spindle during mitosis as an RNA-protein complex that includes 18S ribosomal RNA (PubMed:19596847). In testis, localizes to the chromatoid body (PubMed:23401851). Ubiquitously expressed at low level (PubMed:16713953). Up-regulated in tumors (PubMed:16713953). Dynamically expressed during morphogenesis and in adult skin: in adult skin, expression is up-regulated in the bulge and hair germ as soon as the hair follicle enters its growing phase (anagen) (PubMed:22144916). During anagen, expressed at highest level in cells of the hair germ that give rise to the hair matrix (PubMed:22144916). Detected from 3.5 dpc in the inner cell mass of the blastocyst (PubMed:22144916). Expressed throughout the extra-embryonic ectoderm, which gives rise to the nervous system and epidermis, after implantation and gastrulation (PubMed:22144916). Starting from 9.5 dpc, expression becomes more restricted and at 13.5 and 14.5 dpc it is enriched in developing whiskers and eyes (PubMed:22144916). From 15.5 dpc, when the interfollicular epidermis begins to stratify and follicular morphogenesis starts by forming hair placodes, highest expression is observed in the suprabasal layer of interfollicular epidermis (PubMed:22144916). By Myc (at protein level). Phosphorylated at Ser-139 by AURKB during mitosis, leading to abolish methyltransferase activity and the interaction with NPM1. Mice are viable but show male sterility (PubMed:22144916, PubMed:23401851). Mice display reduced body weight and partial alopecia; alopecia is caused by impaired stem cell differentiation in the epidermis, leading to a delay in initiation of anagen (PubMed:22144916). Mice lacking both Nsun2 and Trdmt1 display a complete loss of cytosine-C5 tRNA methylation, leading to development defects and impaired cellular differentiation causing lethality before P3 (PubMed:22885326). Male sterility is caused by impaired germ cell differentiation in the testis: meiotic progression of germ cells is blocked into the pachytene stage, while spermatogonial and Sertoli cells are unaffected (PubMed:23401851). Belongs to the class I-like SAM-binding methyltransferase superfamily. RsmB/NOP family. TRM4 subfamily. Contaminating sequence. Potential poly-A sequence.