Acid denaturation of DNA in the presence of a polyanion.

Abstract

Abstract 1. 1. Acid denaturation and renaturation of T1 bacteriophage DNA were studied with a view to determine whether the presence of additional polyanions would influence the helix-coil transition under conditions when such influence would be most likely to manifest itself. Polyglucose sulfate, a strong polyanion with high charge density, did not alter the temperature transition even at pH values close to the denaturation pH. Renaturation rates upon cooling were similarly unaffected by the presence of the strong polyanion. Also unaffected were the acid-induced transitions: pH m values and the shape of the transition curves. Similar data were obtained for T2 DNA, as well as for DNA prepared from polyglucose sulfate-inactivated phage. Thus, the generallu accepted practice of disregarding mutual electrostatic effects of various polynucleotide molecules when present in mixture and in high concentration near physiological salt concentration, appears to be justified. 2. 2. In experiments with DNA alone, when the decreasing thermal stability of the helix at decreasing pH values was studied, a close parallel was observed between the lowering of the transition midpoint and the take-up of protons by the bases.