Table 1.
RNA base modifications.
| Canonical Base | Modified Base | Possibility of Non-Enzymatic Generation | Enzymatic Generation | Enzymatic Reversal | Found in VIRUSES |
|---|---|---|---|---|---|
| Adenine | N1-methyladenosine (m1A) | SN2-alkylation | Methyltransferases | AlkB/ALKBH | Yes |
| Adenine | N3-methyladenosine (m3A) | SN2-alkylation | Not known | AlkB/ALKBH | TBD |
| Adenine | N6-methyladenosine (m6A) | Isomerization of m1A | Methyltransferases | AlkB/ALKBH | Yes |
| Adenine | Hypoxanthine base (Inosine ribonucleotide, I) | Low rate spontaneous deamination | Adenine Deaminases Acting on RNA (ADAR) | None | Yes |
| Uracil | Pseudouridine (Ψ) | Not known | Pseudouridine synthase | None | Yes |
| Guanine | N1-methylguanosine (m1G) | SN2-alkylation | Methyltransferases | AlkB/ALKBH | Yes |
| Guanine | N3-methylguanosine (m3G) | SN2-alkylation | Not known | Not known | TBD |
| Guanine | N7-methylguanosine (m7G) | SN2-alkylation | Methyltransferases | Not known | Yes |
| Guanine | O6-methylguanosine (O6mG) | SN1-alkylation | Not known | Not known | TBD |
| Cytosine | N1-methylcytosine (m1C) | SN2-alkylation | Not known | Not known | TBD |
| Cytosine | N3-methylcytosine (m3C) | SN2-alkylation | Not known | AlkB/ALKBH | TBD |
| Cytosine | N5-methylcytosine (m5C) | Not known | Methyltransferases | Not known | Yes |
| Cytosine | Uracil | Spontaneous deamination | APOBEC/AID | None | Yes |