Choice of labeled precursors in synthesis of DNA for molecular hybridization

Tritiated deoxyguanosine triphosphate, labeled in the 8 position of the purine ring, is frequently used as a precursor in the preparation of complementary DNA to be used in molecular hybridization reactions. This compound has been reported to exchange the labeled tritium with water in solution at high temperature. We have investigated the loss of label from DNA prepared with this compound, under conditions commonly used for molecular hybridization reactions. The loss of label follows first order kinetics, with a half time of 17 hrs. under the conditions used. This loss of label influences the reliability of the results of the hybridization reactions, and in some cases may confuse their interpretation. It is recommended that use of complementary DNA labeled with 8-³H]-dGTP be avoided in molecular hybridization experiments.