Structure of a Polycomb Response Element and In Vitro Binding of Polycomb Group Complexes Containing GAGA Factor

Abstract

Polycomb response elements (PREs) are regulatory sites that mediate the silencing of homeotic and other genes. The bxd PRE region from the Drosophila Ultrabithorax gene can be subdivided into subfragments of 100 to 200 bp that retain different degrees of PRE activity in vivo. In vitro, embryonic nuclear extracts form complexes containing Polycomb group (PcG) proteins with these fragments. PcG binding to some fragments is dependent on consensus sequences for the GAGA factor. Other fragments lack GAGA binding sites but can still bind PcG complexes in vitro. We show that the GAGA factor is a component of at least some types of PcG complexes and may participate in the assembly of PcG complexes at PREs.

ACKNOWLEDGMENTS

B.H. and C.T. contributed equally to this work.

We are grateful to Peter Becker and members of his laboratory for the use of his fly cages and help in preparing the wild-type embryonic extract. Thanks are due to Carl Wu and Peter Harte for repeated gifts of antibody, to Gabriella Farkas for the Trl mutants, to Bob Kingston for the LexA-PC gene and to Ivan Dellino for constructing the BP* mutant. We thank Hugh Brock for valuable discussions and for sharing results prior to publication.

This work was supported by a grant from the Swiss National Science Foundation, by the Human Frontiers Science Program, and by a contribution from the Georges and Antoine Claraz Donation.