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The Three-dimensional Architecture of Chromatin In Situ: Electron Tomography Reveals Fibers Composed of a
 

Summary: The Three-dimensional Architecture of Chromatin
In Situ: Electron Tomography Reveals Fibers Composed of a
Continuously Variable Zig-Zag Nucleosomal Ribbon
R. A. Horowitz, D. A. Agard,* J. W. Sedat,* and C. L. Woodcock
Department ofBiology, University of Massachusetts, Amherst, Massachusetts 01003; and *Howard Hughes Medical Institute and
Department of Biochemistry and Biophysics, University ofCalifornia, San Francisco, California94143
Abstract. The three dimensional (3D) structure of
chromatin fibers in sections of nuclei has been deter-
mined using electron tomography. Low temperature
embedding and nucleic acid-specific staining allowed
individual nucleosomes to be clearly seen, and the
tomographic data collection parameters provided a
reconstruction resolution of 2.5 nm. Chromatin fibers
have complex 3D trajectories, with smoothly bending
regions interspersed with abrupt changes in direction,
and U turns. Nucleosomes are located predominantly
at the fiber periphery, and linker DNA tends to pro-
ject toward the fiber interior. Within the fibers, a
unifying structural motif is a two nucleosome-wide
ribbon that is variably bent and twisted, and in which

  

Source: Agard, David - Department of Biochemistry and Biophysics, University of California at San Francisco

 

Collections: Biotechnology; Biology and Medicine