R M Robertson-Anderson

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Oligomeric assembly of Rev on the Rev response element (RRE) is essential for the nuclear export of unspliced and singly spliced human immunodeficiency virus type 1 viral mRNA transcripts. Several host factors, including the human DEAD box protein DDX1, are also known to be required for efficient Rev function. In this study, spontaneous assembly and(More)
Chain topology has a profound impact on the flow behavior of single macromolecules. For circular polymers, the absence of free ends results in a unique chain architecture compared to linear or branched chains, thereby generating distinct molecular dynamics. Here, we report the direct observation of circular DNA dynamics in transient and steady flows for(More)
Using single-molecule fluorescence microscopy and particle-tracking techniques, we elucidate the role DNA topology plays in the diffusion and conformational dynamics of crowded DNA molecules. We focus on large (115 kbp), double-stranded ring and linear DNA crowded by varying concentrations (0-40%) of dextran (10, 500 kDa) that mimic cellular conditions. By(More)
We optically drive a trapped microscale probe through entangled DNA at rates up to 100× the disentanglement rate (Wi≈100), then remove the trap and track subsequent probe recoil motion. We identify a unique crossover to the nonlinear regime at Wi≈20. Recoil dynamics display rate-dependent dilation and complex power-law healing of the reptation tube. The(More)
Despite the ubiquity of molecular crowding in living cells, the effects of crowding on the dynamics of genome-sized DNA are poorly understood. Here, we track single, fluorescent-labeled large DNA molecules (11, 115 kbp) diffusing in dextran solutions that mimic intracellular crowding conditions (0-40%), and determine the effects of crowding on both DNA(More)
We drive optically trapped microspheres through entangled F-actin at constant speeds and distances well beyond the linear regime, and measure the microscale force response of the entangled filaments during and following strain. Our results reveal a unique crossover to appreciable nonlinearity at a strain rate of [small gamma, Greek, dot above]c ≈ 3 s(-1)(More)
We use optical tweezers microrheology and fluorescence microscopy to apply nonlinear microscale strains to entangled and cross-linked actin networks, and measure the resulting stress and actin filament deformations. We couple nonlinear stress response and relaxation to the velocities and displacements of individual fluorescent-labeled actin segments, at(More)
To execute their diverse range of biological functions, RNA molecules must fold into specific tertiary structures and/or associate with one or more proteins to form ribonucleoprotein (RNP) complexes. Single-molecule fluorescence spectroscopy is a powerful tool for the study of RNA folding and RNP assembly processes, directly revealing different(More)
We characterize the scale-dependent rheological properties of mucus from the Chaetopterus sea annelid and determine the intrinsic lengthscales controlling distinct rheological and structural regimes. The mucus produced by this ubiquitous filter feeder serves a host of roles including filtration, protection and trapping nutrients. The ease of clean mucus(More)
We characterize the lengthscale-dependent rheological properties of mucus from the ubiquitous Chaetopterus marine worm. We use optically trapped probes (2-10 μm) to induce microscopic strains and measure the stress response as a function of oscillation amplitude. Our results show that viscoelastic properties are highly dependent on strain scale (l),(More)