What is the role of mismatched uracil glycosylase (Mug) in DNA repair?
The mismatch-specific uracil DNA glycosylase (MUG) belongs to a homologous family of DNA glycosylases that initiate base-excision repair of G:U/T mismatches. The crystal structure of the Mug repair complex points to a preference of Mug for G:U over G:T mispairs. Nonetheless, Mug does not repair U:G or T:G mismatches in vivo. Mug possesses xanthine DNA glycosylase (XDG) activity in E.coli. The repair activity of Mug is more robust against xanthine than uracil. Furthermore, Mug excises the alkylated base, 3, N(4)-ethenocytosine (epsilonC) from epsilonC:G mismatches, and may be the only enzyme in E.coli that can remove this mutagenic adduct. Thus, the principal role of Mug may be the repair of DNA damages caused by exogenous chemical agents such as chloroacetaldehyde.