3-Methyladenine-DNA Glycosylase (MPG Protein) Interacts with Human RAD23 Proteins

Human 3-methyladenine-DNA glycosylase (MPG protein) initiates base excision repair by severing the glycosylic bond of numerous damaged bases. In comparison, homologues of the Rad23 proteins (hHR23) and the hXPC protein are involved in the recognition of damaged bases in global genome repair, a subset of nucleotide excision repair. In this report, we show that the hHR23A and -B also interact with the MPG protein and can serve as accessory proteins for DNA damage recognition in base excision repair. Furthermore, the MPG·hHR23 protein complex elevates the rate of MPG protein-catalyzed excision from hypoxanthine-containing substrates. This increased excision rate is correlated with a greater binding affinity of the MPG protein-hHR23 protein complex for damaged DNA. These data suggest that the hHR23 proteins function as universal DNA damage recognition accessory proteins in both of these major excision repair pathways.