DNA compacted with MukBEF extends in an ordered sequence as each complex releases its loop of DNA.

Bustamante/AAAS

DNA compaction, say Ryan Case, Yun-Pei Chang, Nicholas Cozzarelli, Carlos Bustamante, and colleagues (University of California, Berkeley, CA), may work via a cooperative caterpillar-like mechanism.

The caterpillar is formed by multiple copies of condensin protein—in this case MukBEF—with each V-shaped condensin contributing two legs. Compaction occurs when the caterpillar's legs snap together.

“The main problem,” says Bustamante, “is that we have not had any bulk assay for [the compaction activity of] this protein. We decided to do a rather risky search for a single molecule assay.”

The assay involved binding MukBEF to DNA and then holding both ends of the compacted DNA strand using a dual beam optical trap. As the DNA strand was pulled, it gave way in a sawtooth pattern as individual copies of MukBEF...

The Rockefeller University Press
2004
The Rockefeller University Press
2004
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