Sequence dependence of hydrogen exchange kinetics in DNA duplexes at the individual base pair level in solution.

The kinetics for hydrogen exchange at individual base pairs in self-complementary deoxydodecanucleotide duplexes have been estimated from NMR saturation recovery measurements on the resolved imino protons as a function of temperature. The imino protons of dA . dT base pairs in the center of the fully alternating d(C-G-C-G-T-A-T-A-C-G-C-G) duplex exchange a factor of 2- to 3-fold faster than the corresponding protons at the same positions in the partially alternating d(C-G-C-G-A-A-T-T-C-G-C-G) duplex. These exchange parameters are a direct measure of the rate constants for transient opening of individual dA . dT base pairs in the dodecanucleotide duplexes and demonstrate faster opening kinetics for the "TATA" box region compared to the related "AATT" segment.