The Role of H2A-H2B Dimers in the Mechanical Response of Single Nucleosomes

Abstract

Single-molecule FRET has become a powerful tool to study conformational changes in cellular machines and many other biomolecules. Labeled with fluorophores at specific positions, distance changes can be tracked with high temporal and spatial resolution. Correspondingly, magnetic tweezers have evolved into an important force-based single-molecule technique that allows the manipulation of molecules through piconewton forces in combination with torques. The control over molecular twist is particularly interesting for the study of chiral biomolecules such as double-stranded DNA (dsDNA). Most single-molecule experiments, however, are limited to one of these dimensions of molecular characteristics at a time, leaving some questions unanswered. Simultaneously controlling force and distance in a molecular frame promises to provide a more complete picture of biomolecular interactions. Here, we present a hybrid instrument, combining these two techniques, smFRET and magnetic tweezers, and its application to model systems, such as dsDNA and DNA hairpins. Our experiments demonstrate a parallel force manipulation of several individual biomolecules with forces ranging from 100 fN to 20 pN, while simultaneously recording single fluorophores, leading to an expansion of the available information space.