Single-strand selective monofunctional uracil DNA glycosylase (SMUG1) recognizes breaks in the genome and initiates repair. SMUG1 is a DNA glycosylase specific for uracil (U) residues in DNA, and with a preference for single-stranded DNA substrates. SMUG1 excises uracil and its derivatives [, ]. Its activity is greater towards mismatched U:G than for mismatch U:A [].