Deoxyribonuclease IV from rat liver chromatin and the excision of apurinic sites from depurinated DNA

Deoxyribonuclease IV, a 5′-3′ exonuclease degrading double-stranded DNA from intra-strand nicks, has been purified from the chromatin of rat liver cells. The enzyme, which has an Mr of 58000, excises the apurinic (AP) sites from a depurinated DNA nicked 5′ to these AP sites with the chromatin AP endonuclease. The excision is not the result of hydrolysis of the phosphodiester bond 3′ to the AP sites since the excision product does not behave as deoxyribose 5-phosphate but as its 2,3-unsaturated derivative. This result suggests that, to remove the AP sites from the DNA nicked by an AP endonuclease, the chromatin deoxyribonuclease IV rather acts as a catalyst of beta-elimination.