The lyase activity of the DNA repair protein β-polymerase protects from DNA-damage-induced cytotoxicity

Small DNA lesions such as oxidized or alkylated bases are repaired by the base excision repair (BER) pathway1. BER includes removal of the damaged base by a lesion-specific DNA glycosylase, strand scission by apurinic/apyrimidinic endonuclease, DNA resynthesis and ligation2. BER may be further subdivided into DNA β-polymerase (β-pol)-dependent single-nucleotide repair and β-pol-dependent or -independent long patch repair subpathways3,4,5,6. Two important enzymatic steps in mammalian single-nucleotide BER are contributed by β-pol: DNA resynthesis of the repair patch and lyase removal of 5′-deoxyribose phosphate (dRP)2. Fibroblasts from β-pol null mice are hypersensitive to monofunctional DNA-methylating agents, resulting in increases in chromosomal damage, apoptosis and necrotic cell death3,7. Here we show that only the dRP lyase activity of β-pol is required to reverse methylating agent hypersensitivity in β-pol null cells. These results indicate that removal of the dRP group is a pivotal step in BER in vivo. Persistence of the dRP moiety in DNA results in the hypersensitivity phenotype of β-pol null cells and may signal downstream events such as apoptosis and necrotic cell death.