De novo synthesis of a polymer of deoxyadenylate and deoxythymidylate by calf thymus DNA polymerase alpha.

In a reaction mixture containing calf thymus DNA polymerase alpha (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase; EC 2.7.7.7), calf thymus DNA unwinding protein, DNA, deoxyadenosine 5'-triphosphate and deoxythymidine 5'-triphosphate, a copolymer of deoxyadenylate and deoxythymidylate is synthesized after a lag period of 1-2 hr. In the presence of the four deoxyribonucleoside triphosphates only deoxyadenylate and deoxythymidylate are incorporated into the polymer and the rate of synthesis is decreased. The reaction variably occurs in the absence of DNA or DNA unwinding protein but with a greatly entended lag period. The optimal Mg2+ concentration for synthesis of the polymer of deoxyadenylate and deoxythymidylate is 1 mM, in contrast to an optimal Mg2+ concentration of 8 mM for DNA synthesis with activated DNA as template. Characterization of the product of de novo synthesis indicates that it is the alternating copolymer, poly(dA-dT).