Nucleosome binding and histone methyltransferase activity of Drosophila PRC2

Abstract

The Drosophila Polycomb group protein E(z) is a histone methyltransferase (HMTase) that is essential for maintaining HOX gene silencing during development. E(z) exists in a multiprotein complex called Polycomb repressive complex 2 (PRC2) that also contains Su(z)12, Esc and Nurf55. Reconstituted recombinant PRC2 methylates nucleosomes in vitro, but recombinant E(z) on its own shows only poor HMTase activity on nucleosomes. Here, we investigate the function of the PRC2 subunits. We show that PRC2 binds to nucleosomes in vitro but that individual PRC2 subunits alone do not bind to nucleosomes. By analysing PRC2 subcomplexes, we show that Su(z)12-Nurf55 is the minimal nucleosome-binding module of PRC2 and that Esc contributes to high-affinity binding of PRC2 nucleosomes. We find that nucleosome binding of PRC2 is not sufficient for histone methylation and that only complexes that contain Esc protein show robust HMTase activity. These observations suggest that different subunits provide mechanistically distinct functions within the PRC2 HMTase: the nucleosome-binding subunits Su(z)12 and Nurf55 anchor the E(z) enzyme on chromatin substrates, whereas Esc is needed to boost enzymatic activity.

Dynamic regulatory interactions of Polycomb group genes: MEDEA autoregulation is required for imprinted gene expression in Arabidopsis

“…Down-regulation in fis mutants could be due to an excess-of-silencing mediated by mutant forms of PcG proteins, as described for the Tritorax-mimick mutant allele of E(z) in Drosophila (LaJeunesse and Shearn 1996;Bajusz et al 2001). This seems unlikely, however, because the lesions in the mea-1, fis2-1, and fie-2 alleles used in this study (Grossniklaus et al 1998;Luo et al 1999;Ohad et al 1999) cause truncation in the SET, VEFS, and WD40 domains of MEA, FIS2, and FIE, respectively, which are essential to the formation of a functional PcG complex (Denisenko et al 1998;Cao and Zhang 2004;Chanvivattana et al 2004;Yamamoto et al 2004;Nekrasov et al 2005). Instead, it is likely that MEA, FIS2, and FIE directly or indirectly activate FIS2, FIE, and MSI1 expression.…”

LHP1, the Arabidopsis homologue of HETEROCHROMATIN PROTEIN1, is required for epigenetic silencing of FLC

“…This model predicts the involvement of a number of factors that have not yet been identified in the genetic analysis of vernalization. In the PRC2 complex, Su(z)12 is thought to confer nucleosome binding, whereas the H3K27 histone methyltransferase activity depends predominantly on ENHANCER OF ZESTE [E(z)] (13). An E(z) function may therefore be associated with the VRN2 complex.…”

From Flies to Mice: The Emerging Role of Non-Canonical PRC1 Members in Mammalian Development

“…The histone methyltransferase activity of PRC2 is connected to the SET domain of the E(Z) protein, but E(Z) protein is not catalytically active alone [111]. The E(Z)/EZH2 subunits has to be complexed with at least the ESC/EED and SUZ12 homolog subunits to be catalytically active [112][113][114][115][116]. Additional facultative subunits such as PCL [117], Jumonji, AT rich interactive domain 2 (JARID2) [118] and AE binding protein 2 (AEBP2) were shown to target variant PRC2 complexes, and further enhance their catalytic activity [119].…”