Table 1. Methyl modifications to RNA.

Name	Short name	Modified edge	Found on mRNA	Typical location
2’-O-methyladenosine	Am	Sugar	Yes	Cap1, Cap2
2’-O-methylcytidine	Cm	Sugar	Yes	Cap1, Cap2
2’-O-methylguanosine	Gm	Sugar	Yes	Cap1, Cap2
2’-O-methyluridine	Um	Sugar	Yes	Cap1, Cap2
N6,2’-O-dimethyladenosine	m6Am	Sugar and Watson–Crick	Yes	Cap1
1-methyladenosine	m1A	Watson–Crick	Yes	Internal
1-methylguanosine	m1G	Watson–Crick	Yes	Internal
5-methylcytidine	m5C	Watson–Crick	Yes	Internal
N6-methyladenosine	m6A	Watson–Crick	Yes	Internal
7-methylguanosine	m7G	Watson–Crick	Yes	Cap structure (Cap0, Cap1, Cap2)
7-methylguanosine cap (cap 0)	m7Gpp(pN)	Watson–Crick	Yes	Cap structure (Cap0, Cap1, Cap2)
N2,N2,7-trimethylguanosine	m2,2,7G	Watson–Crick	No	Cap structure (snRNA)
N2,N2,7-trimethylguanosine cap (cap TMG)	m2,2,7Gpp(pN)	Watson–Crick	No	Cap structure (snRNA)
N2,N2-dimethylguanosine	m2,2G	Watson–Crick	No	Cap structure (snRNA)
N2,7-dimethylguanosine	m2,7G	Watson–Crick	No	Cap structure (snRNA)
N2,7-dimethylguanosine cap (cap DMG)	m2,7Gpp(pN)	Watson–Crick	No	Cap structure (snRNA)
N4-acetyl-2’-O-methylcytidine	ac4Cm	Sugar and Watson–Crick	No
5-carboxymethylaminomethyl-2’-O-methyluridine	cmnm5Um	Sugar and Watson–Crick	No
5-formyl-2’-O-methylcytidine	f5Cm	Sugar and Watson–Crick	No
1,2’-O-dimethylguanosine	m1Gm	Sugar and Watson–Crick	No
1,2’-O-dimethylinosine	m1Im	Sugar and Watson–Crick	No
N2,N2,2’-O-trimethylguanosine	m2,2Gm	Sugar and Watson–Crick	No
N2,7,2’-O-trimethylguanosine	m2,7Gm	Sugar and Watson–Crick	No
N2,2’-O-dimethylguanosine	m2Gm	Sugar and Watson–Crick	No
3,2’-O-dimethyluridine	m3Um	Sugar and Watson–Crick	No
N4,N4,2’-O-trimethylcytidine	m4,4Cm	Sugar and Watson–Crick	No
N4,2’-O-dimethylcytidine	m4Cm	Sugar and Watson–Crick	No
5,2’-O-dimethylcytidine	m5Cm	Sugar and Watson–Crick	No
5,2’-O-dimethyluridine	m5Um	Sugar and Watson–Crick	No
N6,N6,2’-O-trimethyladenosine	m6,6Am	Sugar and Watson–Crick	No
isowyosine	imG2	Watson–Crick	No
5-carboxymethylaminomethyl-2- thiouridine	cmnm5s2U	Watson–Crick	No
5-carboxymethylaminomethyl-2-selenouridine	cmnm5se2U	Watson–Crick	No
5-carboxymethylaminomethyluridine	cmnm5U	Watson–Crick	No
5-cyanomethyluridine	cnm5U	Watson–Crick	No
2’-O-methylinosine	Im	Sugar	No
1-methyl-3-(3-amino-3-carboxypropyl)pseudouridine	m1acp3Y	Watson–Crick	No
1-methylinosine	m1I	Watson–Crick	No
1-methylpseudouridine	m1Y	Watson–Crick	No
2,8-dimethyladenosine	m2,8A	Watson–Crick	No
2-methyladenosine	m2A	Watson–Crick	No
N2-methylguanosine	m2G	Watson–Crick	No
3-methylcytidine	m3C	Watson–Crick	No
3-methyluridine	m3U	Watson–Crick	No
3-methylpseudouridine	m3Y	Watson–Crick	No
N4,N4-dimethylcytidine	m4,4C	Watson–Crick	No
N4-methylcytidine	m4C	Watson–Crick	No
5-methyldihydrouridine	m5D	Watson–Crick	No
5-methyl-2-thiouridine	m5s2U	Watson–Crick	No
5-methyluridine	m5U	Watson–Crick	No
N6,N6-dimethyladenosine	m6,6A	Watson–Crick	No
N6-methyl-N6-threonylcarbamoyladenosine	m6t6A	Watson–Crick	No
8-methyladenosine	m8A	Watson–Crick	No
5-methoxycarbonylmethyl-2’-O-methyluridine	mcm5Um	Sugar and Watson–Crick	No
methylwyosine	mimG	Watson–Crick	No
5-methylaminomethyl-2-thiouridine	mnm5s2U	Watson–Crick	No
5-methylaminomethyl-2-selenouridine	mnm5se2U	Watson–Crick	No
5-methylaminomethyluridine	mnm5U	Watson–Crick	No
2-methylthio-N6-methyladenosine	ms2m6A	Watson–Crick	No
5-carbamoylmethyluridine	ncm5U	Watson–Crick	No
5-carbamoylmethyl-2’-O-methyluridine	ncm5Um	Sugar and Watson–Crick	No
5-aminomethyl-2-thiouridine	nm5s2U	Watson–Crick	No
5-aminomethyl-2-selenouridine	nm5se2U	Watson–Crick	No
5-aminomethyluridine	nm5U	Watson–Crick	No
2-thio-2’-O-methyluridine	s2Um	Watson–Crick	No
5-taurinomethyl-2-thiouridine	tm5s2U	Watson–Crick	No
5-taurinomethyluridine	tm5U	Watson–Crick	No
2’-O-methylpseudouridine	Ym	Sugar	No

Initial list taken from MODOMICS ⁶, redundant entries removed (for example, m7G and m7Gppp considered the same for the purpose of this review). Entries are annotated with simple information including: The modified edge of the nucleotide (i.e. whether the methyl group is found on the base itself or the sugar); the species of RNA the modification is normally found on; and the typical position of the modified nucleotide along an mRNA transcript where relevant..