Long patch base excision repair compensates for DNA polymerase β inactivation by the C4'-oxidized abasic site

Area of Science:

• Molecular Biology
• DNA Repair Mechanisms
• Biochemistry

Background:

• The C4'-oxidized abasic site (C4-AP) is a DNA lesion formed by various damaging agents.
• This lesion is known for its mutagenic and reactive properties, leading to interstrand cross-links.

Purpose of the Study:

• To investigate the base excision repair pathway for DNA containing C4-AP.
• To understand the interaction of DNA polymerase β and Ape1 with the C4-AP lesion.

Main Methods:

• Enzymatic assays examining the incision of C4-AP by Ape1.
• Analysis of DNA polymerase β activity on C4-AP in different DNA contexts (ternary complexes, duplexes, single-stranded DNA).
• Investigation of C4-AP's effect on DNA polymerase β enzyme stability and turnover.

Main Results:

• Ape1 incises C4-AP approximately 12-fold less efficiently than a standard apurinic/apyrimidinic lesion.
• DNA polymerase β mediates β-elimination of incised C4-AP, with the fastest excision occurring in ternary complexes.
• The C4-AP lesion inactivates DNA polymerase β after about seven turnovers due to reaction with active site lysine residues.
• Unlike other inhibitors, C4-AP is removed by strand displacement synthesis involving DNA polymerase β and flap endonuclease 1.

Conclusions:

• DNA polymerase β plays a dual role in C4-AP repair, facilitating excision but also being inactivated by the lesion.
• The inactivation of DNA polymerase β by C4-AP may contribute to the cytotoxicity of drugs that generate this lesion.
• Understanding C4-AP repair is crucial for comprehending DNA damage responses and drug-induced toxicity.