The proteins, called condensins, are important for a variety of housekeeping processes in chromosomes, but the mechanics behind their function have been largely unknown. When the researchers alternately stretched and compressed a single molecule of DNA with condensins attached, they found that the DNA extended in stepwise "clicks," akin to Velcro unzipping.
The successful manipulation of a single DNA molecule with condensin proteins attached makes it plausible to think about using a similar strategy to explore the machinery that processes chromosomes in the cell, said one of the study's senior authors, Carlos Bustamante, a Howard Hughes Medical Institute researcher at the University of California, Berkeley.
Bustamante, Ryan B. Case, Nicholas R. Cozzarelli and their colleagues at Berkeley published their findings on June 3, 2004, in Science Express, which provides rapid electronic publication of selected articles from the journal Science.
"Until now, little was known about the function of condensins," said Bustamante. "It was known that if the gene for the protein was knocked out, chromosomes failed to segregate properly in cell division. One daughter cell might receive all the DNA and the other none."
Bustamante and his colleagues took note of earlier studies by another group of researchers that provided evidence that condensins appeared to induce "supercoiling" in DNA, which occurs when two helical molecules intertwine.
"We decided to try to develop a single-molecule assay, to see whether we could really understand the mechanism of this protein's effects on DNA," said Bustamante. "Even though there was no bulk as
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
4-Jun-2004