Mammalian 5-Formyluracil−DNA Glycosylase. 2. Role of SMUG1 Uracil−DNA Glycosylase in Repair of 5-Formyluracil and Other Oxidized and Deaminated Base Lesions†

In the accompanying paper [Matsubara, M., et al. (2003) Biochemistry 42, 4993−5002], we have partially purified and characterized rat 5-formyluracil (fU)−DNA glycosylase (FDG). Several lines of evidence have indicated that FDG is a rat homologue of single-strand-selective monofunctional uracil−DNA glycosylase (SMUG1). We report here that rat and human SMUG1 (rSMUG1 and hSMUG1) expressed from the corresponding cDNAs indeed excise fU in single-stranded (ss) and double-stranded (ds) DNA. The enzymes also excised uracil (U) and uracil derivatives bearing an oxidized group at C5 [5-hydroxyuracil (hoU) and 5-hydroxymethyluracil (hmU)] in ssDNA and dsDNA but not analogous cytosine derivatives (5-hydroxycytosine and 5-formylcytosine) and other oxidized damage. The damage specificity and the salt concentration dependence of rSMUG1 (and hSMUG1) agreed well with those of FDG, confirming that FDG is rSMUG1. Consistent with the damage specificity above, hSMUG1 removed damaged bases from Fenton-oxidized calf thymus DNA...