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Molecular and Cellular Biology, October 2001, p. 6585-6597, Vol. 21, No. 19
Department of Biological Chemistry and
Molecular Pharmacology, Harvard Medical School, Boston,
Massachusetts 02115
Received 10 April 2001/Returned for modification 21 May
2001/Accepted 28 June 2001
The Polycomb group proteins are responsible for long-term
repression of a number of genes in Drosophila
melanogaster, including the homeotic genes of the bithorax
complex. The Polycomb protein is thought to alter the
chromatin structure of its target genes, but there has been little
direct evidence for this model. In this study, the chromatin structure
of the bithorax complex was probed with three separate assays for
DNA accessibility: (i) activation of polymerase II (Pol II)
transcription by Gal4, (ii) transcription by the bacteriophage T7 RNA
polymerase (T7RNAP), and (iii) FLP-mediated site-specific
recombination. All three processes are restricted or blocked
in Polycomb-repressed segments. In contrast, control test sites outside of the bithorax complex permitted Gal4,
T7RNAP, and FLP activities throughout the embryo. Several P insertions in the bithorax complex were tested, providing evidence that the Polycomb-induced effect is widespread over target genes.
This accessibility effect is similar to that seen for SIR silencing in
Saccharomyces cerevisiae. In contrast to SIR
silencing, however, episomes excised from
Polycomb-repressed chromosomal sites do not show an
altered superhelix density.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.19.6585-6597.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Polycomb Group Repression Reduces DNA
Accessibility
*
Corresponding author. Mailing address: Department of
Biological Chemistry and Molecular Pharmacology, Harvard Medical
School, Boston, MA 02115. Phone: (617) 432-1906. Fax: (617) 738-0516.
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