It was revealed by thorough study of the T.T*(C-1)<-> T.T(C-1) tautomerisation via the synchronous concerted double proton transfer (DPT) through the TS (C-2v) that the T.T*/T*.T H-bonded mismatch is dynamically stable non-planar complex with a lifetime 1.6 x 10(-10) s. The 5 key points were firstly detected and completely investigated along the intrinsic reaction coordinate of the DPT tautomerisation. The reported data allow us to suggest that the T/mutagenic tautomer of the thymine (T) is shared with approximately equal probability between two DNA strands during the dissociation of the mispair by DNA polymerase. (C) 2013 Elsevier B.V. All rights reserved.