Hydrogen-exchange kinetics in a double-helical polynucleotide with the adenine-uracil basepair A use of the N6-methyladenine residue

The kinetics of hydrogen-tritium exchange reactions have been followed, using a Sephadex technique, for a double-helical $\text{poly(ribo}\text{-N}{}^6\text{-}\text{methyladenylic acid)-poly(ribouridylic acid)}$ complex. Only one (but not two) hydrogen in every $\text{N}{}^6\text{-}\text{methyladenine}\text{·}\text{uracil}$ basepair has been found to exchange at a measurably slow rate (1.2 · 10⁻³ s⁻¹) at 0°C. Thus, the proton exchange between the adenine-amino and uracil-imide groups in a double-helical polynucleotide is considered to be not as fast as has been suggested previously (approx. 10 s⁻¹) for an adenine · uracil basepair in a monomer system in a non-polar solvent.