Molecular and Cellular Biology, October 1998, p. 5992-6000, Vol. 18, No. 10
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
-Globin Locus but Not the Maintenance of an
Open Chromatin Structure in Erythroid Cells
andDivision of Basic Science, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109,1 and Department of Radiation Oncology, University of Washington Medical School, Seattle, Washington 981952
Received 19 May 1998/Accepted 30 June 1998
Studies in many systems have led to the model that the human
-globin locus control region (LCR) regulates the transcription, chromatin structure, and replication properties of the
-globin locus. However the precise mechanisms of this regulation are unknown. We have developed strategies to use homologous recombination in a
tissue culture system to examine how the LCR regulates the locus in its
natural chromosomal environment. Our results show that when the
functional components of the LCR, as defined by transfection and
transgenic studies, are deleted from the endogenous
-globin locus in
an erythroid background, transcription of all
-globin genes is
abolished in every cell. However, formation of the remaining hypersensitive site(s) of the LCR and the presence of a DNase I-sensitive structure of the
-globin locus are not affected by the
deletion. In contrast, deletion of 5'HS5 of the LCR, which has been
suggested to serve as an insulator, has only a minor effect on
-globin transcription and does not influence the chromatin structure
of the locus. These results show that the LCR as currently defined is
not necessary to keep the locus in an "open" conformation in
erythroid cells and that even in an erythroid environment an open locus
is not sufficient to permit transcription of the
-like globin genes.
Present address: Department of Medicine, Arizona Cancer Center,
University of Arizona, Tucson, AZ 85724.
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