How your body packs a metre of DNA inside every cell

Several views of a 3-dimensional computer model of dna packing in a nucleosome.
Several views of a 3-dimensional computer model of DNA packing in a nucleosome.
Credit: Bednar et al.

It’s one of those statistics that makes you pause – or win the pub trivia contest, depending on your lifestyle.

Human cells that carry a full complement of DNA range in volume from a very tiny 130 cubic micrometres for a white blood cell to a comparatively massive 600,000 cubic micrometres for a fat cell.

But even at the top end of the scale, cells are very tiny things. A micrometre, after all, is just one millionth of a metre.

Yet here’s the thing: every cell in the body (bar sperm, eggs, and red blood cells) contains a whole metre of DNA.

Just how we have evolved to manage this sort of TARDIS-like achievement is now a little clearer, thanks to research conducted by a team led by Jeffrey Hayes of the University of Rochester School of Medicine and Dentistry in New York, US.

Hayes and his team set out to discover exactly how such a great length of genetic material could be packed into super-tight cell spaces.

To do that, they looked closely at the nucleosome, the most basic building block of chromosomes – the rigid framework that holds the DNA.

The team identified a target protein, known as linker histone H1 – or H1, for short – which the scientists suspected played a key role in inducing chromosomes to be inflexible and compact.

Hayes recruited fellow researchers in France and Japan to take high-magnification X-ray images of H1 and other DNA proteins in an effort to better understand the mechanisms involved. The resulting images were useful, but the resolution was insufficient to enable unambiguous interpretation.

To the rescue came co-author Amber Cutter, who conducted a series of test-tube experiments using a range of DNA proteins. The result, added to the information obtained through the X-rays, was clear: with H1, chromosomes were tight and strong; without it, they were long and floppy.

Apart from its use as a storage enabler, Hayes and his team suggest the protein may have a protective effect, buffering DNA from deforming pressure, and shielding it from physical damage.

The research is published in the journal Molecular Cell.

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