Ultraslow relaxation of confined DNA

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Science  25 Jul 2014:
Vol. 345, Issue 6195, pp. 380-381
DOI: 10.1126/science.1256359

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Polymers are ubiquitous and occur in many diverse forms, including cross-linked synthetic polymers (e.g., rubber and plastic) and biopolymers such as DNA and proteins. DNA has long been used as a model system for polymer science because long, chemically well-defined DNA chains can be prepared using its ability to self-replicate, and because it can be analyzed at the single-molecule level. For instance, the relaxation dynamics of a distorted DNA molecule eventually reverting to its lowest-energy configuration have been investigated extensively (1). There has been growing interest in understanding the relaxation of spatially confined polymers. How biopolymers such as DNA and proteins behave under high spatial confinement is important because they often experience such conditions—for example, when DNA passes through a narrow pore during viral packaging or bacterial conjugation. With the advent of nanotechnology (DNA is 2 nm in diameter), it has now become possible to study the relaxation dynamics of DNA confined in one (2) and two (3) dimensions. Berndsen et al. (4) have undertaken the first characterization of DNA relaxation under extreme confinement in three dimensions. Remarkably, they find that DNA relaxation under such circumstances is slowed by a factor of more than 60,000, presenting a daunting challenge for the biological machines that need to compact DNA reliably into tight spaces.