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MBC in Press, published online ahead of print October 12, 2005
Mol. Biol. Cell 10.1091/mbc.E05-04-0321

A more recent version of this article appeared on January 1, 2006
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Submitted on April 18, 2005
Revised on September 29, 2005
Accepted on October 4, 2005

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

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 5 and 6-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.

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






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