A nucleosome is the basic repeating unit of eukaryotic chromatin. In a human cell, about six feet of DNA must be packaged into a nucleus with a diameter less than a human hair. A single nucleosome consists of about 150 base pairs of DNA sequence wrapped around a core of histone proteins. The nucleosomes are arranged like beads on a string. They are repeatedly folded in on themselves to form a chromosome.
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The nucleosomes are structural building blocks of the packing of DNA within a chromosome. The packing problem of how to fit a very, very long stretch of DNA, which is about a yard of DNA, inside a very small cell, which is about a hundredth of a millimeter in diameter, has fascinated scientists for a long time. And it turns out how the cell does this--now--remember that each cell in the body has this problem--is that it coils and super coils the DNA in a multitude of complex ways. The fundamental building block of that coiling are nucleosomes, which are blocks of essentially little spheres of histone proteins around which the DNA is wrapped, and they look literally like beads on a string, except the beads have the DNA wrapped around them instead of having the DNA go through them, as in the case of a bead on a string.
Christopher P. Austin, M.D.
Director, NIH Chemical Genomics Center (NCGC); Senior Advisor for Translational Research, Office of the Director
Dr. Austin's research focuses on development of reagents and technologies to translate genome sequence into functional insights. As director of the NIH Chemical Genomics Center (NCGC), part of a network of screening centers that produce chemical probes for use in biological research and drug development, Dr. Austin is spearheading a chemical genomics program that brings the power of small-molecule chemistry and informatics to the elucidation of gene function. Just as the Human Genome Project accelerated gene identification, this initiative promises to speed discoveries on gene function and lead to the development of new therapies for human disease.