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Molecular and Cellular Biology, November 1998, p. 6584-6594, Vol. 18, No. 11
Department of Chemistry and Biochemistry, University of
California, Los Angeles, Los Angeles, California
90095-15691;
Department of Genetics,
University of Adelaide, Adelaide, South Australia 5005, Australia2; and
Rockefeller
University Protein/DNA Technology Center, New York, New York
100213
Received 29 June 1998/Returned for modification 2 August
1998/Accepted 17 August 1998
Dorsal functions as both an activator and repressor of
transcription to determine dorsoventral fate in the Drosophila
melanogaster embryo. Repression by Dorsal requires the
corepressor Groucho (Gro) and is mediated by silencers termed ventral
repression regions (VRRs). A VRR in zerknüllt
(zen) contains Dorsal binding sites as well as an essential
element termed AT2. We have identified and purified an AT2 DNA binding
activity in embryos and shown it to consist of cut
(ct) and dead ringer (dri) gene
products. Studies of loss-of-function mutations in ct and
dri demonstrate that both genes are required for the
activity of the AT2 site. Dorsal and Dri both bind Gro, acting
cooperatively to recruit it to the DNA. Thus, ventral repression may
require the formation of a multiprotein complex at the VRR. This
complex includes Dorsal, Gro, and additional DNA binding proteins,
which appear to convert Dorsal from an activator to a repressor by
enabling it to recruit Gro to the template. By showing how binding site
context can dramatically alter transcription factor function, these
findings help clarify the mechanisms responsible for the regulatory
specificity of transcription factors.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Dorsal-Mediated Repression Requires the Formation of a
Multiprotein Repression Complex at the Ventral Silencer

*
Corresponding author. Mailing address: Department of
Chemistry and Biochemistry, UCLA, 405 Hilgard Ave., Los Angeles, CA
90095-1569. Phone: (310) 825-2530. Fax: (310) 206-4038. E-mail:
courey{at}chem.ucla.edu.
Present address: Novartis Biotechnology, Research Triangle Park, NC
27709.
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