The Drosophila esc and E(z) Proteins Are Direct Partners in Polycomb Group-Mediated Repression

ABSTRACT

The extra sex combs (esc) and Enhancer of zeste [E(z)] proteins are members of the Drosophila Polycomb group (Pc-G) of transcriptional repressors. Here we present evidence for direct physical interaction between the esc and E(z) proteins using yeast two-hybrid and in vitro binding assays. In addition, coimmunoprecipitation from embryo extracts demonstrates association of esc and E(z) in vivo. We have delimited the esc-binding domain of E(z) to an N-terminal 33-amino-acid region. Furthermore, we demonstrate that site-directed mutations in the esc protein previously shown to impair esc function in vivo disrupt esc-E(z) interactions in vitro. We also show an in vitro interaction between the heed and EZH1 proteins, which are human homologs of esc and E(z), respectively. These results suggest that the esc-E(z) molecular partnership has been conserved in evolution. Previous studies suggested that esc is primarily involved in the early stages of Pc-G-mediated silencing during embryogenesis. However, E(z) is continuously required in order to maintain chromosome binding by other Pc-G proteins. In light of these earlier observations and the molecular data presented here, we discuss how esc-E(z) protein complexes may contribute to transcriptional silencing by the Pc-G.

ACKNOWLEDGMENTS

We thank Susan Strome for valuable discussions, comments on the manuscript, and sharing information prior to publication. We thank Gloria Lee for providing heed cDNA and for sharing information prior to publication, Ken Abel for providingEZH1 cDNAs, and Justin Goodrich for sharing unpublished information. We thank Yong Ma, Ellen Miller, and Chris Schwartz for generating plasmid constructs used in this work. We thank Doug Bornemann for input on GST pull-down experiments and Andre Silvanovich and Tom Hays for advice on epitope tag reagents. We thank Judy Berman for comments on the manuscript.

This work was supported by NIH grant GM49850 to J.S. and NIH grant GM46567 to R.S.J.