p55 is a common component of many chromatin-modifying complexes and has been
shown to bind to histones. Here, we present a crystal structure of Drosophila
p55 bound to a histone H4 peptide. p55, a predicted WD40 repeat protein,
recognizes the first helix of histone H4 via a binding pocket located on the
side of a beta-propeller structure. The pocket cannot accommodate the histone
fold of H4, which must be altered to allow p55 binding. Reconstitution
experiments show that the binding pocket is important to the function of
p55-containing complexes. These data demonstrate that WD40 repeat proteins use
various surfaces to direct the modification of histones.
