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Originally published as MBC in Press, 10.1091/mbc.E05-04-0321 on October 12, 2005

Vol. 17, Issue 1, 104-113, January 2006

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Proteolysis of Mitotic Chromosomes Induces Gradual and Anisotropic Decondensation Correlated with a Reduction of Elastic Modulus and Structural Sensitivity to Rarely Cutting Restriction Enzymes

Lisa H. Pope, Chee Xiong, and John F. Marko

Department of Physics, University of Illinois at Chicago, Chicago, IL 60607-7059

Submitted April 18, 2005; Revised September 29, 2005; Accepted October 4, 2005
Monitoring Editor: Joseph Gall

The effect of nonspecific proteolysis on the structure of single isolated mitotic newt chromosomes was studied using chromosome elastic response as an assay. Exposure to either trypsin or proteinase K gradually decondensed and softened chromosomes but without entirely eliminating their elastic response. Analysis of chromosome morphology revealed anisotropic decondensation upon digestion, with length increasing more than width. Prolonged protease treatment resulted only in further swelling of the chromosome without complete dissolution. Mild trypsinization induced sensitivity of chromosome elasticity to five- and six-base-specific restriction enzymes. These results, combined with previous studies of effects of nucleases on mitotic chromosome structure, indicate that mild proteolysis gradually reduces the density of chromatin-constraining elements in the mitotic chromosome, providing evidence consistent with an anisotropically folded "chromatin network" model of mitotic chromosome architecture.

This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E05–04–0321) on October 12, 2005.

Abbreviations used: DTT, dithiothreitol; PBS, phosphate-buffered saline; RE, restriction enzyme; SMC, structural maintenance of chromosomes protein.

Address correspondence to: J. F. Marko (jmarko{at}uic.edu).






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