The components of the system are MutS, which binds to the GT mismatch, the VSR endonuclease, which cuts the DNA, and MutL, which recruits the UvrD helicase.

Hence, the VSR endonucleases have a function to protect the cell from damage caused by mutated DNA.

VSR recognises a TG mismatched base pair, generated after spontaneous deamination of methylated cytosines, and it creates a nick on a single strand by cleaving the phosphate backbone on the 5' side of the thymine.

In Escherichia coli, this endonuclease nicks double-stranded DNA within the sequence CT(AT)GN or NT(AT)GG next to the thymidine residue, which is mismatched to 2'-deoxyguanosine.

[4] VSR has three aromatic residues (Phe67, Trp68 and Trp86), which intercalate into the major groove, bending the DNA and separating the two strands.