DNA glycosylase that excises thymine from T/G mismatches. Also has a weak DNA glycosylase activity on uracil paired with various bases. Hydrolyzes mismatched double-stranded DNA and polynucleotides, releasing free thymine. Binds 1 [4Fe-4S] cluster. The cluster has a structural role. Thymine cleavage is completely inhibited by Ni(2+), Co(2+), Zn(2+), Cu(2+) and Mn(2+). Activity is not affected by Mg(2+) and Ca(2+). Optimum pH is 8.5. Optimum temperature is 65-70 degrees Celsius. Belongs to the Nth/MutY family.