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Molecular and Cellular Biology, July 1999, p. 5189-5202, Vol. 19, No. 7
Department of Microbiology and Immunology,
Kimmel Cancer Center, Thomas Jefferson University, Philadelphia,
Pennsylvania 19107
Received 15 December 1998/Returned for modification 21 January
1999/Accepted 13 April 1999
In Drosophila, two classes of genes, the
trithorax group and the Polycomb group, are
required in concert to maintain gene expression by regulating chromatin
structure. We have identified Trithorax protein (TRX) binding elements
within the bithorax complex and have found that within the
bxd/pbx regulatory region these elements are functionally
relevant for normal expression patterns in embryos and confer TRX
binding in vivo. TRX was localized to three closely situated sites
within a 3-kb chromatin maintenance unit with a modular structure.
Results of an in vivo analysis showed that these DNA fragments (each
~400 bp) contain both TRX- and Polycomb-group response elements (TREs
and PREs) and that in the context of the endogenous
Ultrabithorax gene, all of these elements are essential for
proper maintenance of expression in embryos. Dissection of one of these
maintenance modules showed that TRX- and Polycomb-group responsiveness
is conferred by neighboring but separable DNA sequences, suggesting
that independent protein complexes are formed at their respective
response elements. Furthermore, we have found that the activity of this
TRE requires a sequence (~90 bp) which maps to within several tens of
base pairs from the closest neighboring PRE and that the PRE activity
in one of the elements may require a binding site for PHO, the protein
product of the Polycomb-group gene
pleiohomeotic. Our results show that long-range maintenance
of Ultrabithorax expression requires a complex element
composed of cooperating modules, each capable of interacting with both
positive and negative chromatin regulators.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Trithorax- and Polycomb-Group Response Elements
within an Ultrabithorax Transcription Maintenance Unit
Consist of Closely Situated but Separable Sequences
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson
University, Room 485, Jefferson Alumni Hall, 1020 Locust St.,
Philadelphia, PA 19107. Phone: (215) 503-4785. Fax: (215) 923-7144. E-mail: mazo{at}lac.jci.tju.edu.
This work is dedicated to the memory of Tadaatsu Goto.
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