The Polycomb Group Protein Complex of Drosophila melanogaster Has Different Compositions at Different Target Genes

Abstract

In Drosophila the Polycomb group genes are required for the long-term maintenance of the repressed state of many developmental regulatory genes. Their gene products are thought to function in a common multimeric complex that associates with Polycomb group response elements (PREs) in target genes and regulates higherorder chromatin structure. We show that the chromodomain of Polycomb is necessary for protein-protein interactions within a Polycomb-Polyhomeotic complex. In addition, Posterior Sex Combs protein coimmunoprecipitates Polycomb and Polyhomeotic, indicating that they are members of a common multimeric protein complex. Immunoprecipitation experiments using in vivo cross-linked chromatin indicate that these three Polycomb group proteins are associated with identical regulatory elements of the selector gene engrailed in tissue culture cells. Polycomb, Polyhomeotic, and Posterior Sex Combs are, however, differentially distributed on regulatory sequences of the engrailed-related gene invected. This suggests that there may be multiple different Polycomb group protein complexes which function at different target sites. Furthermore, Polyhomeotic and Posterior Sex Combs are also associated with expressed genes. Polyhomeotic and Posterior Sex Combs may participate in a more general transcriptional mechanism that causes modulated gene repression, whereas the inclusion of Polycomb protein in the complex at PREs leads to stable silencing.

Set Domain-Dependent Regulation of Transcriptional Silencing and Growth Control by SUV39H1, a Mammalian Ortholog of Drosophila Su(var)3-9

“…(5,37). Consistent with this possible mechanism, SUV39H1 associates with M31 (HP1␤), the only other characterized mammalian su(var) homolog (1), and their cosedimentation supports participation in a su(var) complex distinct from two previously described mammalian PcG complexes (45,46). When SUV39H1 is forcibly expressed under our experimental conditions, it accumulates in distinct nuclear bodies that are large and electron dense, with ultrastructural features suggestive of heterochromatin.…”

“…The repressor property of SUV39H1 localized to its amino-terminal half which also contains a chromo domain, a modular motif that self-associates and assembles into multimeric complexes on chromatin (31,39,46). Notably, transcriptional repression by SUV39H1 did not require its SET domain.…”

“…The Su(var)3-9 protein and its mammalian ortholog SUV39H1 are unique in being the only characterized PEV modifiers that share two of these consensus motifs, the chromo and SET domains (1, 50). Chromo domains are 40-amino-acid modular motifs that are implicated in protein self-association (8) and the assembly of site-specific multimeric complexes on chromatin (39,46). SET domains are 130-amino-acid motifs named for three proteins in which they were originally identified: Su(var)3-9, Enhancer-of-zeste, and Trithorax (25).…”

Adaptive selection and coevolution at the proteins of the Polycomb repressive complexes in Drosophila

“…In contrast, Context Mirror predicts the PHO/SFMBT interaction (Alfieri et al, 2013) and the well-characterized interactions between these two subunits of the PhoRC complex and those of PRC1: PHO/PC (Mohd-Sarip et al, 2002), PHO/PH-P (Mohd- Sarip et al, 2002) and SFMBT/SCM (Grimm et al, 2009). The bioinformatic method also predicts the well-established interactions between subunits of the PRC1 complex, that is, PH-P/PC (Strutt and Paro, 1997), PH-P/PSC (Kyba and Brock, 1998), PH-P/SCM (Peterson et al, 1997), PC/PSC (Kyba and Brock, 1998), PC/SCE and PSC/SCE (Gorfinkel et al, 2004). In contrast, no interaction is predicted between the two subunits of the PR-DUB complex, although the N-terminal region of ASX is directly involved in its interaction with CALYPSO (Scheuermann et al, 2010).…”

Comparing active and repressed expression states of genes controlled by the Polycomb/Trithorax group proteins

“…The advent of ChIP maps demonstrated an accumulation of PcG/TrxG proteins at PREs and some of the associated promoters (18,19). Interestingly, PcG proteins were found to be bound at PREs, even if the associated gene was active (20,21). In addition, a recent study that concentrated on the HOX gene Ultrabithorax (Ubx) in Drosophila imaginal discs showed that members of the PRC1/2 complexes and Trx are constitutively bound at the regulatory sites of Ubx regardless of its activity state (16).…”