But researchers at the University of Illinois at Chicago have discovered it is not protein, but chromatin, the portion of the cell nucleus that contains DNA, which provides this support.
"What we've shown is that the mitotic form of chromosomes, when they're folded up for transmission during cell division -- the long, chromatin fibers made of DNA complexed with a lot of protein -- are linked at cross-link points, kind of like playground monkey bars," said John Marko, associate professor of physics at UIC. "And the bars are just chromatin."
The findings will be reported in the online edition of the Proceedings of the National Academy of Sciences the week of Oct. 28.
Marko, who also holds a courtesy appointment in bioengineering, was assisted by Michael Poirier, a former Ph.D. student in physics at UIC, who is now doing post-doctoral research at the Universit Louis Pasteur in Strasbourg, France.
Marko and Poirier discovered the protein-support idea literally did not hold up following a series of experiments involving newt chromosomes, chosen because they are large and easy to grasp and manipulate under the microscope. After treating the chromosomes with low concentrations of enzymes that cut DNA at specific points, they discovered there was no support left, and the chromosomes dissolved.
The chromosomes were removed from cells and held in place by hair-like glass tube pipettes. The DNA digestion was done in free solution. This methodology was never previously used. The technique may prove useful in unlocking the puzzle of how cells divide.