Maxim Y. Sheinin

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DNA melting under torsion plays an important role in a wide variety of cellular processes. In the present Letter, we have investigated DNA melting at the single-molecule level using an angular optical trap. By directly measuring force, extension, torque, and angle of DNA, we determined the structural and elastic parameters of torsionally melted DNA. Our(More)
The response of single DNA molecules to externally applied forces and torques was directly measured using an angular optical trap. Upon overwinding, DNA buckled abruptly as revealed by a sharp extension drop followed by a torque plateau. When the DNA was held at the buckling transition, its extension hopped rapidly between two distinct states. Furthermore,(More)
The nucleosome, the fundamental packing unit of chromatin, has a distinct chirality: 147 bp of DNA are wrapped around the core histones in a left-handed, negative superhelix. It has been suggested that this chirality has functional significance, particularly in the context of the cellular processes that generate DNA supercoiling, such as transcription and(More)
As a single DNA molecule is positively supercoiled under constant tension, its extension initially increases due to a negative twist-stretch coupling. The subsequent attainment of an extension maximum has previously been assumed to be indicative of the onset of a phase transition from B- to scP-DNA. Here we show that an extension maximum in fact does not(More)
Methods for exerting and measuring forces on single molecules have revolutionized the study of the physics of biology. However, it is often the case that biological processes involve rotation or torque generation, and these parameters have been more difficult to access experimentally. Recent advances in the single-molecule field have led to the development(More)
As the fundamental packing units of DNA in eukaryotes, nucleosomes play a central role in governing DNA accessibility in a variety of cellular processes. Our understanding of the mechanisms underlying this complex regulation has been aided by unique structural and dynamic perspectives offered by single molecule techniques. Recent years have witnessed(More)
While slowly turning the ends of a single molecule of DNA at constant applied force, a discontinuity was recently observed at the supercoiling transition when a small plectoneme is suddenly formed. This can be understood as an abrupt transition into a state in which stretched and plectonemic DNA coexist. We argue that there should be discontinuities in both(More)
A dynamical system is said to exhibit hysteresis if its current state depends on its history. Muscle shows hysteretic properties at constant length, such as residual force enhancement after stretch. There is no generally accepted explanation for residual force enhancement. Here we examine a very simple kinetic model for the interaction between actin and(More)
Note that Ceff is a function of force: there is less “softening” at higher forces. In the experiments of Forth et al., the renormalized Ceff was measured directly via the torque. However, the range of applied forces was small enough that Ceff did not change appreciably, and a single value of C = (89 nm)kT was quoted. Here, we also use the same renormalized(More)