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Single molecules of double-stranded DNA (dsDNA) were stretched with force-measuring laser tweezers. Under a longitudinal stress of approximately 65 piconewtons (pN), dsDNA molecules in aqueous buffer undergo a highly cooperative transition into a stable form with 5.8 angstroms rise per base pair, that is, 70% longer than B form dsDNA. When the stress was(More)
Here we use mechanical force to induce the unfolding and refolding of single RNA molecules: a simple RNA hairpin, a molecule containing a three-helix junction, and the P5abc domain of the Tetrahymena thermophila ribozyme. All three molecules (P5abc only in the absence of Mg2+) can be mechanically unfolded at equilibrium, and when kept at constant force(More)
Single DNA molecules were chemically attached by one end to a glass surface and by their other end to a magnetic bead. Equilibrium positions of the beads were observed in an optical microscope while the beads were acted on by known magnetic and hydrodynamic forces. Extension versus force curves were obtained for individual DNA molecules at three different(More)
Supplemental figure Ia Velocity vs. time for a packaging complex held under a constant load of ~5 pN. Velocity was determined by linear fitting in a 1 s sliding window. These data correspond to the black line shown in Fig. 1b. b, To determine the experimental noise, velocity vs. time was also obtained for a 15 kb long DNA molecule that was directly attached(More)
Titin, a giant filamentous polypeptide, is believed to play a fundamental role in maintaining sarcomeric structural integrity and developing what is known as passive force in muscle. Measurements of the force required to stretch a single molecule revealed that titin behaves as a highly nonlinear entropic spring. The molecule unfolds in a high-force(More)
The ribosome translates the genetic information encoded in messenger RNA into protein. Folded structures in the coding region of an mRNA represent a kinetic barrier that lowers the peptide elongation rate, as the ribosome must disrupt structures it encounters in the mRNA at its entry site to allow translocation to the next codon. Such structures are(More)
Helicases are a ubiquitous class of enzymes involved in nearly all aspects of DNA and RNA metabolism. Despite recent progress in understanding their mechanism of action, limited resolution has left inaccessible the detailed mechanisms by which these enzymes couple the rearrangement of nucleic acid structures to the binding and hydrolysis of ATP. Observing(More)
This paper reports a study of the deposition process of DNA molecules onto a mica surface for imaging under the scanning force microscope (SFM). Kinetic experiments indicate that the transport of DNA molecules from the solution drop onto the surface is governed solely by diffusion, and that the molecules are irreversibly adsorbed onto the substrate. A(More)
DNA wrapped in nucleosomes is sterically occluded, creating obstacles for proteins that must bind it. How proteins gain access to DNA buried inside nucleosomes is not known. Here we report measurements of the rates of spontaneous nucleosome conformational changes in which a stretch of DNA transiently unwraps off the histone surface, starting from one end of(More)