A major challenge in chromatin biology is to understand the mechanisms by which 
chromatin is remodeled into active or inactive states as required during 
development and cell differentiation. One complex implicated in these processes 
is the nucleosome remodeling and histone deacetylase (NuRD) complex, which 
contains both histone deacetylase and nucleosome remodeling activities and has 
been implicated in the silencing of subsets of genes involved in various stages 
of cellular development. Chromodomain-helicase-DNA-binding protein 4 (CHD4) is a 
core component of the NuRD complex and contains a nucleosome remodeling ATPase 
domain along with two chromodomains and two plant homeodomain (PHD) fingers. We 
have previously demonstrated that the second PHD finger of CHD4 binds peptides 
corresponding to the N terminus of histone H3 methylated at Lys(9). Here, we 
determine the solution structure of PHD2 in complex with H3K9me3, revealing the 
molecular basis of histone recognition, including a cation-π recognition 
mechanism for methylated Lys(9). Additionally, we demonstrate that the first PHD 
finger also exhibits binding to the N terminus of H3, and we establish the 
histone-binding surface of this domain. This is the first instance where histone 
binding ability has been demonstrated for two separate PHD modules within the 
one protein. These findings suggest that CHD4 could bind to two H3 N-terminal 
tails on the same nucleosome or on two separate nucleosomes simultaneously, 
presenting exciting implications for the mechanism by which CHD4 and the NuRD 
complex could direct chromatin remodeling.