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"If these plasmids don't divide and go to the next generation of cells, those bacteria cells lose their drug resistance," Schumacher notes.

In the Nature paper, the scientists capture the first structure ever solved of a segrosome complex that partitions and divides DNA.

A protein called ParR connects with a centromere DNA site, a round string of DNA repeats in the plasmid, to form the segrosome complex, which then completes itself by attracting filaments of another protein called ParM. The ParM filaments grow, literally pushing the two replicated plasmid segrosomes apart, resulting in two copies of the plasmid with intact DNA.

"An important question in segregation biology has been 'what structure does the segrosome adopt"' Our segrosome structure answers that question. We now have a molecular model for the segregation of DNA," Schumacher says.

Solving the structure is necessary to understand how these molecules function. "If we know these details we can design highly specific drugs to disrupt their actions," Schmacher notes.

The researchers used a technique called X-ray crystallography to discern the structure of both proteins connecting to the plasmid DNA. This technique first requires purification and crystallization of the protein or, in this case, the more challenging DNA-protein complex structure. These are usually the most difficult steps of the process.

Next, the crystal sample is mounted on a tiny loop in an X-ray diffractor and X-rays are beamed through it. Bending around the lattice of atoms in the crystal, the X-rays produce a diffraction pattern, which can be seen as a dot pattern on a monitor.

A state-of-the-art X-ray diffracto
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