Chromatin-modifying Complex Component Nurf55/p55 Associates with Histones H3 and H4 and Polycomb Repressive Complex 2 Subunit Su(z) 12 through Partially Overlapping Binding Sites

Drosophila Nurf55 is a component of different chromatin-modifying complexes, including the PRC2(Polycomb repressive complex 2). Based on the 1.75-angstrom crystal structure of Nurf55 bound to histone H4 helix 1, we analyzed interactions of Nurf55 (Nurf55 or p55 in fly and RbAp48/46 in human) with the N-terminal tail of histone H3, the first helix of histone H4, and an N-terminal fragment of the PRC2 subunit Su(z) 12 using isothermal calorimetry and pulldown experiments. Site-directed mutagenesis identified the binding site of histone H3 at the top of the Nurf55 WD40 propeller. Unmodified or K9me3- or K27me3-containing H3 peptides were bound with similar affinities, whereas the affinity for K4me3-containing H3 peptides was reduced. Helix 1 of histone H4 and Su(z) 12 bound to the edge of the beta-propeller using overlapping binding sites. Our results show similarities in the recognition of histone H4 and Su(z) 12 and identify Nurf55 as a versatile interactor that simultaneously contacts multiple partners.