Direct reversal repair (direct repair of DNA) is a single step reaction of removal of the methyl- or photoadduct.
1. Methylphosphotriesters - direct removal of the alkyl damage by nucleophilic Cys residues.
Direct repair O6-alkylguanine by Ada (E.coli)
2. DNA Alkyltransferases
Direct repair of O6-alkylguanine by MGMT (H.sapiens)
Direct repair of O4-Alkylthymine by Ogt (E.coli)
3. Oxidative dealkylation
AlkB proteins (E.coli, H.sapiens)
4. Photolyase - direct reversal of the thymine dimer created by UV light
CTD photolyase (E.coli, S.cerevisiae)