Polymerase Incorporation and Miscoding Properties of 5-Chlorouracil

Inflammation-mediated hypochlorous acid (HOCl) can damage DNA, DNA precursors, and other biological molecules, thereby producing an array of damage products such as 5-chlorouracil (ClU). In this study, we prepared and studied 5-chloro-2'-deoxyuridine (CldU) and ClU-containing oligonucleotide templates. We demonstrate that human K-562 cells grown in culture with 10 mu M CldU incorporate substantial amounts of CldU without significant toxicity. When in the template, ClU residues pair with dATP but also with dGTP, in a pH-dependent manner with incorporation by human polymerase beta, avian myeloblastosis virus reverse transcriptase (AMV-RT), and Escherichia call Klenow fragment (exo(-)) polymerase. The enhanced miscoding of ClU is attributed to the electron-withdrawing 5-chlorine substituent that promotes the formation of an ionized ClU-G mispair. When mispaired with G, ClU is targeted for removal by human glycosylases. The formation, incorporation, and repair of ClU could promote transition mutations and other forms of heritable DNA damage.