Dna Denaturation-Supercoiling Transition at Thermophilic Temperatures

Abstract

Local DNA opening plays an important role in DNA metabolism and cell biology as the double-helix must be melted before the information contained within may be accessed. Cells finely tune the torsional state of their genomes to strike a balance between stability and accessibility. For example, while thermophilic organisms maintain relaxed or positively supercoiled genomes, mesophilic life forms use unique mechanisms to maintain a negatively supercoiled genome. Here, we use a single-molecule magnetic tweezers approach at high temperature to quantify the force-dependent equilibrium between DNA melting and supercoiling at temperatures populated by Thermophiles. We show that negatively supercoiled DNA denatures at 0.5 pN lower tension at thermophilic vs. mesophilic temperatures. This work demonstrates the ability to monitor DNA supercoiling at high temperature and opens the possibility to perform magnetic tweezers assays on thermophilic systems. More speculatively, the data provide a physical rationale for the evolution of negative supercoiling and suggest that the average DNA tension in vivo lies between 0.3 - 1.1 pN.