Here’s how cells rapidly stuff two meters of DNA into microscopic capsules | Science News

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Here’s how cells rapidly stuff two meters of DNA into microscopic capsules

Two proteins form loops and a spiral helix that facilitate speedy packing

4:30pm, January 29, 2018
simulation of bundled chromosomes

PACK IT UP  Before dividing, a cell bundles each of its chromosomes (gray and colored strings in this simulation of a single chromosome) into a tightly-packed, orderly cylinder. A protein that creates a central, spiral scaffold (red links) is partly responsible for the efficient packing, a new study finds.

Frequent fliers, take note. Scientists have figured out how cells quickly pack long chromosomes into compact, organized bundles — a key step before cells divide. The new finding unifies two competing ideas about the process: whether it involves winding chromosomes into a spiral staircase or into a set of loops. It turns out cells use two different ring-shaped proteins called condensins to do both actions, imaging and computer simulations reveal.

Normally, chromosomes sit unspooled in a cell’s nucleus. But when a cell prepares to undergo mitosis — a type of cell division — those strings of DNA must condense into easy-to-transfer cylinders. It’s a formidable task: A cell must cram about two meters of DNA into microscopic packages without tangling the genetic material like a string of holiday lights.

Condensin II shapes a chromosome into large loops and then forms a helical scaffold for the loops to wind around. Condensin I subdivides large

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