Excision repair (修補馬路vs填補馬路)excision repair: can be happened in the DNA that are not in replication. -nucleotide excision repair. (修補馬路)repair endonuclease (uvrABCendonuclease). ex, to remove TT dimer, or to remove a segment of DNA contains the mutated one.-base excision repair. (類似填補馬路)DNA glycosylase: remove damage site to form AP sites.AP endonuclease: to remove the apurinicor apyrimidinicsites (AP sites).Many mutagen can cause the AP site formationDirect repair (填補馬路)-By photoactivation:ex, UV damage. TT dimer by photoactivation(visible light) and catalyzed by photolyase.-By alkyltransferase: ex, DNA mutagen. repair the alky group (CnH2n+1)