Conformational Transitions of Polynucleotides in Polymer Media

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Abstract
The melting temperature of three polynucleotides, poly(deoxyadenylic‐thymidylicf‐acid (double helix), calf‐thymus DNA and Staphylococcus aureus phage 80α DNA, increases in the presence of two neutral polymers, dextran and poly(ethyleneglycol). The results have been interpreted as a steric exclusion phenomenon. Two strands of polynucleotides in random coil conformation occupy a larger volume than a helix structure and the equilibrium between the two conformational forms is therefore moved towards the formation of the more compact helix when the available volume in the solution is restricted. The experiments indicate that steric exclusion in polymer media can influence the conformation of other macromolecules.