Enzymatic synthesis of deoxyribonucleic acid. XII. A polymer of deoxyguanylate and deoxycytidylate.

The enzyme deoxyribonucleic acid polymerase, purified from Escherichia coli, catalyzes extensive formation of deoxyribonucleic acid by a mechanism that involves replication of a deoxyribonucleic acid primer. This replication requires the presence of the four deoxynucleoside triphosphates commonly found in deoxyribonucleic acid, and deoxyribonucleic acid itself (1). In the absence of one, two, or three of the deoxynucleoside triphosphates, a limited reaction occurs, which represents the addition of only one or very few deoxynucleotide residues to the deoxynucleoside end of the primer deoxyribonucleic acid molecule (2). Both the extensive and limited reactions occur without lag and are detectable only when deoxyribonucleic acid has been added. Two reactions have now been discovered which are exceptions t,o this rule. They are observed after lug periods and occur in the absence of added DNA. As judged by viscometric, sedimentation, and spectrophotometric studies, the products, like DNA. are rigid, hydrogen-bonded macromolecules. In one case, already described (3), the product is a copolymer (dAT)l composed exclusively of deoxyadenylate and deoxythymidylate in exactly alternating sequence. In the second case, the subject of this report, the product contains only deoxyguanylate and deoxycytidylate arranged as hydrogen-bonded homopolymers (dGdC). When either polymer, dAT or dGdC, is isolated and used as a primer for the enzymatic reaction, a shortened lag period occurs, which is related inversely to the amount of primer added (4)) and extensive synthesis of an identical polymer results. In this report we shall describe the synthesis and properties of dGdC polymer and an analogous polymer, dGdBC. The accompanying report describes studies on the kinetics and mechanism of synthesis of dAT and dGdC polymers (4).