Structural studies of heterochromatin protein 1 (HP1) interaction with chromatin . (360G-Wellcome-094519_Z_10_Z)

HP1, which exists as three homodimeric isoforms (HP1alpha, beta, gamma), plays a critical role in constitutive heterochromatin, regulation of the expression of heterochromatic and euchromatic genes, and DNA repair. The monomer unit comprises a chromodomain (CD), a homologous chromoshadow domain (CSD), which dimerises, and a connecting hinge region of variable length. Most attention has focussed on binding of HP1 through its CD to the epigenetic mark H3K9Me, but this does not explain all aspec ts of HP1 binding to chromatin. We will focus mainly on two other regions in HP1 the CSD, which interacts with nucleosomal histone H3 at a second (occluded) site in a methylation-independent manner; and the hinge region, which interacts with DNA in vitro. Building on our preliminary work we will determine the structure of the HP1α CSD in complex with a peptide containing the second H3 site by NMR, and characterise the structure and the DNA-binding properties of the HP1 hinge region. We wi ll also study the interaction of full length HP1 with histones H3 and H1, and through a combination of biochemistry and novel NMR we will characterise the nature of HP1 binding to chromatin.