Polycomb group (PcG) proteins maintain the transcriptional silence of target genes through many cycles of cell division. Here, we provide evidence for the sequential binding of PcG proteins at a Polycomb response element (PRE) in proliferating cells in which the sequence-specific DNA binding Pho and Phol proteins directly recruit E(z)-containing complexes, which in turn methylate histone H3 at lysine 27 (H3mK27). This provides a tag that facilitates binding by a Pc-containing complex. In wing imaginal discs, these PcG proteins also are present at discrete locations at or downstream of the promoter of a silenced target gene, Ubx. E(z)-dependent H3mK27 is also present near the Ubx promoter and is needed for Pc binding. The location of E(z)- and Pc-containing complexes downstream of the Ubx transcription start site suggests that they may inhibit transcription by interfering with assembly of the preinitiation complex or by blocking transcription initiation or elongation.
|Original language||English (US)|
|Number of pages||10|
|State||Published - Jun 4 2004|
Bibliographical noteFunding Information:
We thank Mark Mortin for helpful comments on the manuscript and we thank Judith Benes for excellent technical assistance. We thank Jeff Simon, Michael Atchison, Haiming Chen, and Rob Harrod for providing plasmids and we thank Rob White for providing anti-Ubx antibody. We also thank Rob Harrod for assistance with confocal microscopy. This work was supported by NIH grants GM46567 (to R.S.J.) and GM068804 (to Y.Z.).