Excises ethenocytosine and uracil, which can arise by alkylation or deamination of cytosine, respectively, from the corresponding mispairs with guanine in ds-DNA. It is capable of hydrolyzing the carbon-nitrogen bond between the sugar-phosphate backbone of the DNA and the mispaired base. The complementary strand guanine functions in substrate recognition. Required for DNA damage lesion repair in stationary-phase cells. Specifically hydrolyzes mismatched double-stranded DNA and polynucleotides, releasing free uracil. Binds DNA as a monomer. Belongs to the uracil-DNA glycosylase (UDG) superfamily. TDG/mug family.