Table 2.

The major steps and protein participants in BER.

BER STEP	PROTEIN	BIOCHEMICAL ACTIVITY	DNA SUBSTRATE
GLYCOSYLASE	UNG	Glycosylase	U
	SMUG1	Glycosylase	U, hydroxyU, hydroxymethylU
	MBD4	Glycosylase	U or T opposite G at CpG sites
	TDG	Glycosylase	U, T or ethenoC opposite G
	OGG1	Glycosylase, AP β-lyase	8-oxoG opposite C, FAPY
	MYH/MUTYH	Glycosylase	A opposite 8-oxoG
	NTH/NTHL1	Glycosylase, AP β-lyase	Ring saturated or fragmented Py
	MPG	Glycosylase	3-MeA, ethenoA, hypoxanthine
	NEIL1	Glycosylase, AP β,δ-lyase	Tg, FAPY, hydroxyU
	NEIL2	Glycosylase, AP β,δ-lyase	Oxidized Py
	NEIL3	Glycosylase	Oxidized Py
AP ENDONUCLEASE	APE1	AP endonuclease	AP site
STRAND BREAK PROCESSING	POLβ	5′-dRP lyase	5′-dRP
	APE1	3′-Phosphodiesterase	3′-α,β-Unsaturated aldehyde
	PNKP	3′-Phosphatase/5′-Kinase	3′-Phosphate, 5′-hydroxyl
	TDP1	3′-Phosphodiesterase	3′-Protein (TopoI)
	APRATAXIN	5′-Hydrolase	5′-AMP
POLYMERIZATION	POLβ	Gap-filling polymerase	DNA Gap (1–6 nt)
	POLδ (POLε)	Strand-displacement polymerase	DNA strand break
	FEN1	5′-Flap endonuclease	5′-Flap
LIGATION	XRCC1/LIG3α	Ligase complex	DNA nick
	LIG1	Ligase	DNA nick

AP=apurinic/apyrimidinic; U=uracil; T=thymine; C=cytosine; G=guanine; FAPY=formamidopyrimidine; Py = pyrimidine; dRP = deoxyribose phosphate.