TABLE 2.

Writers, erasers, and readers for m5C.

Effect	Protein name	Cellular location	Effect on RNA methylation and its mechanisms	Evidence related to SLE
Writers (methyltransferase)	DNMT2/TRDMT1	Nucleus and cytosol	Mainly mediates the m5C modification of DNA and tRNA Raddatz et al., 2013	–
	NSUN2	1. G1 phase: nucleolus 2. S phase: between nucleolus and nucleoplasm 3. G2 phase: cytoplasm, M phase: centrioles	Modifies some non-coding small RNAs and tRNA Khoddami and Cairns, 2013	The expression of NSUN2 was decreasing in CD4+ T cells from patients with SLE compared with healthy controls Guo et al., 2020.
	NSUN5		Mediates the m5C modification of human 28S rRNA Janin et al., 2019	–
	TRM4B		Involved in tRNA methylation and recognition Cui X. et al., 2017; David et al., 2017	–
Erasers (demethylase)	TET2	Nucleus	Involved in 5-methylcytidine oxidation Xue C. et al., 2020	Silencing of the TET2 gene obviously diminishes follicular helper T cell polarization in vitro, which plays a critical role in SLE Wu et al., 2016.
Readers (methylation recognition protein)	ALYREF	Nucleus	Involved in mRNA nuclear-cytoplasmic shuttling, viral RNA export and replication Xue C. et al., 2020
	Cytoplasmic YBX1	Cytoplasm	Involved in mRNA stabilization, embryogenesis and tumorigenesis Xue C. et al., 2020
	TRM4B		Involved in tRNA methylation and recognition Cui X. et al., 2017; David et al., 2017

DNMT2/TRDMT1, DNA methyltransferase E2/tRNA aspartic acid methyltransferase 1; NSUN2, NOL1/NOP2/SUN domain methyltransferase family2; NSUN5, NOL1/NOP2/SUN, domain methyltransferase family5; TRM4B, tRNA-specific methyltransferase 4B; TET2, ten-eleven translocation 2; ALYREF, Aly/REF output factor; YBX1, Y-box binding protein 1.