Annual Report 2002 - Cornell University
003 Selected Faculty Research

21 Pulling apart chromatin fiber for observation

Michelle D. Wang, Physics, and research team made the first direct observation of the dynamic structure of individual nucleosomes—basic genetic packaging units. Chromosomal DNA is packaged into the compact structure of the nucleosome along with specialized proteins called histones. The DNA complex and histones are called chromatin in the cells of higher organisms. Wang's team used optical tweezers to pull apart individual strands of chromatin. They were able to see how information in nucleosomes becomes accessible to the molecules that read it. The researchers proposed a three-stage model for how nucleosomal units in chromatin open to reveal their DNA to enzymes such as RNA polymerase, which moves along the DNA molecule transcribing the genetic information for use by the cell. Nucleosomes seem to prevent the genetic information-transfer process that happens a million times a day in the cells of our bodies. Researchers want to understand the mechanical barrier presented by the nucleosome and how the nucleosome structure is modified to clear the way for information transfer. Although the basic plan of the system is previous knowledge, the structural and biophysical details of the system have not been clear.

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