A reversible change in the location of a hydrogen atom in a molecule that alters it from one to another isomer. Thymine and guanine are normally in keto forms, but when in the rare enol forms (see diagram) they can join by three hydrogen bonds with keto forms of guanine or thymine, respectively.

What is a tautomeric shift in DNA?

The spontaneous isomerization of a nitrogen base to an alternative hydrogen-bonding form, possibly resulting in a mutation. Reversible shifts of proton position in a molecule. bases in nucleic acids shift between keto and enol forms or between amino and imino forms.

What is a tautomeric shift and what type of mutation does it cause?

A tautomeric shift in one strand has produced a transition mutation in the complementary strand. If the mutation occurs in the germline, it will be transmitted to future generations. IMPORTANT: Note that a tautomeric shift is not itself a mutation, but a transient change to an alternative form of the molecule.