Electrophoresis of Chromatin on Nondenaturing Agarose Gels Containing Mg2+
SELF-ASSEMBLY OF SMALL CHROMATIN FRAGMENTS AND FOLDING OF THE 30-nm FIBER (*)
- From the Departament de Bioquímica i Biologia Molecular, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain
- ¶ To whom correspondence should be addressed: Dept. de Bioquímica i Biologia Molecular, Facultat de Ciències (Edifici C-s), Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain . Tel.: 34-3-5811616; Fax: 34-3-5811264.
Abstract
We show that nondenaturing agarose gels can be used for the study of the structure and dynamic properties of native (uncross-linked)
chromatin. In gels containing 1.7 mM Mg
, chicken erythrocyte chromatin fragments having from about 6 to 50 nucleosomes produce well defined bands. These bands have
an electrophoretic mobility that decreases only slightly with molecular weight. This surprising behavior is not observed in
low ionic strength gels. Fragments with less than 6 nucleosomes and low content of histones H1-H5 give rise to broad bands
in gels with Mg
. In contrast, fragments containing only 3-4 nucleosomes but with the normal H1-H5 content are able to form associated structures
with a mobility similar to that observed for high molecular weight chromatin. Electron microscopy results indicate that the
associated fragments and the fragments of higher molecular weight show similar electrophoretic properties because they become
very compact in the presence of Mg
and form cylindrical structures with a diameter of 
33 nm. Our results suggest that the interactions involved in the self-assembly of small fragments are the same that direct
the folding of larger fragments; in both cases, the resulting compact chromatin structure is formed from a basic element containing
5-7 nucleosomes.
Footnotes
-
↵§ Recipient of a predoctoral fellowship from the Generalitat de Catalunya.
-
↵* This work was supported in part by a Grants PB89-0305 and PB92-0602 from the Dirección General de Investigación Científica y Técnica. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- bp
-
base pair(s)
- kb
-
kilobase pair(s)
- PMSF
-
phenylmethylsulfonyl fluoride.
-
- Received May 15, 1995.
- Revision received June 30, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
