Catalysis of the removal of mismatched pyrimidine bases in DNA. Enzymes with this activity recognize and remove pyrimidines present in mismatches by cleaving the N-C1' glycosidic bond between the target damaged DNA base and the deoxyribose sugar. The reaction releases a free base and leaves an apyrimidinic (AP) site.
G/T-mismatch-specific thymine-DNA glycosylase activity