Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

CHROMOSOMAL DNA AND ITS PACKAGING IN THE CHROMATIN FIBER
189
Figure 4–23 The structure of a nucleosome
core particle, as determined by x-ray
diffraction analyses of crystals. Each
histone is colored according to the scheme in
Figure 4–22, with the DNA double helix in light
gray. (Adapted from K. Luger et al., Nature
389:251–260, 1997. With permission from
Macmillan Publishers Ltd.)
DNA double helix
side view
edge view
histone H2A histone H2B histone H3 histone H4
neutralize the negatively charged DNA backbone. These numerous interactions
explain in part why DNA of virtually any sequence can be bound on a histone
octamer core. The path of the DNA around the histone core is not smooth; rather,
several kinks are seen in the DNA, as expected from the nonuniform surface of the
(A)
H2A
N
C
H2B
H3
N
N
MBoC6 m4.24/4.22
C
C
H4
N
C
N-terminal tail
histone fold
(B)
(D)
N
N
C
N
(C)
N
histone
octamer
C
N
N
C
N
N
N
N
N
Figure 4–24 The overall structural organization of the core histones. (A) Each of the core
histones contains an N-terminal tail, which is subject to several forms of covalent modification, and
a histone fold region, as indicated. (B) The structure of the histone fold, which is formed by all four
of the core histones. (C) Histones 2A and 2B form a dimer through an interaction known as the
“handshake.” Histones H3 and H4 form a dimer through the same type of interaction. (D) The final
histone octamer on DNA. Note that all eight N-terminal tails of the histones protrude from the discshaped
core structure. Their conformations are highly flexible, and they serve as binding sites for
sets of other proteins.