ABSTRACT

Because the exocyclic amino groups of the DNA bases mediate base pairing, their loss is mutagenic. The amino groups are subject to attack by normal intracellular compounds as well as by environmental agents, and the types of enzymes that are involved in their repair are universal. This chapter focuses on the enzymatic repair of deaminated purines in DNA, specifically hypoxanthine (deaminated adenine) and xanthine (deaminated guanine). The pyrimidines cytosine and 5-methylcytosine are deaminated by many of the same agents as the purines, and so the causes and consequences of their deamination are also discussed. Their repair, however, is covered in separate chapters (Chapters 1, 14, and 22). 5-Hydroxyuracil (derived from cytosine) and 5-hydroxymethyluracil (derived from 5-methylcytosine or thymidine) are oxidation products and are separately covered (Chapter 15). The repair of deaminated bases in DNA, including deaminated oxidation products, has been previously reviewed (1).