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Molecular and Cellular Biology, October 2000, p. 7572-7582, Vol. 20, No. 20
Departments of
Pathology,1 Genetics and
Development,2 Biochemistry and Molecular
Biophysics,5 and
Medicine,7 Columbia University College
of Physicians and Surgeons, New York, New York 10032; Institute
of Immunology and Molecular Genetics, Karlsruhe D-76133,
Germany3; Institute of Molecular
Biology and Genetics and Department of Molecular Biology, Seoul
National University, Seoul 151-742, Korea4;
and Molecular Biology Program, Memorial Sloan-Kettering
Cancer Center, New York, New York 100216
Received 17 February 2000/Returned for modification 12 April
2000/Accepted 12 July 2000
We have previously described a SWI/SNF-related protein complex (PYR
complex) that is restricted to definitive (adult-type) hematopoietic
cells and that specifically binds DNA sequences containing long
stretches of pyrimidines. Deletion of an intergenic DNA-binding site
for this complex from a human
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
An Ikaros-Containing Chromatin-Remodeling Complex
in Adult-Type Erythroid Cells
-globin locus construct results in
delayed human
- to
-globin switching in transgenic mice,
suggesting that the PYR complex acts to facilitate the switch. We now
show that PYR complex DNA-binding activity also copurifies with
subunits of a second type of chromatin-remodeling complex,
nucleosome-remodeling deacetylase (NuRD), that has been shown to have
both nucleosome-remodeling and histone deacetylase activities. Gel
supershift assays using antibodies to the ATPase-helicase subunit of
the NuRD complex, Mi-2 (CHD4), confirm that Mi-2 is a component of the
PYR complex. In addition, we show that the hematopoietic
cell-restricted zinc finger protein Ikaros copurifies with PYR complex
DNA-binding activity and that antibodies to Ikaros also supershift the
complex. We also show that NuRD and SWI/SNF components coimmunopurify
with each other as well as with Ikaros. Competition gel shift
experiments using partially purified PYR complex and recombinant Ikaros
protein indicate that Ikaros functions as a DNA-binding subunit of the
PYR complex. Our results suggest that Ikaros targets two types of
chromatin-remodeling factors
activators (SWI/SNF) and repressors
(NuRD)
in a single complex (PYR complex) to the
-globin locus in
adult erythroid cells. At the time of the switch from fetal to adult
globin production, the PYR complex is assembled and may function to
repress
-globin gene expression and facilitate
- to
-globin switching.
*
Corresponding author. Mailing address: Department of
Genetics and Development, Hammer Health Sciences Room 1604, 701 West 168th Street, New York, NY 10032. Phone: (212) 305-4186. Fax: (212)
923-2090. E-mail: bank{at}cuccfa.ccc.columbia.edu.
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