The chromodomain, helicase, DNA-binding protein 5 (CHD5) is a chromatin 
remodeling enzyme which is implicated in tumor suppression. In this study, we 
demonstrate the ability of the CHD5 PHD fingers to specifically recognize the 
unmodified N-terminus of histone H3. We use two distinct modified 
peptide-library platforms (beads and glass slides) to determine the detailed 
histone binding preferences of PHD(1) and PHD(2) alone and the tandem PHD(1-2) 
construct. Both domains displayed similar binding preferences for histone H3, 
where modification (e.g., methylation, acetylation, and phosphorylation) at 
H3R2, H3K4, H3T3, H3T6, and H3S10 disrupts high-affinity binding, and the three 
most N-terminal amino acids (ART) are crucial for binding. The tandem 
CHD5-PHD(1-2) displayed similar preferences to those displayed by each PHD 
finger alone. Using NMR, surface plasmon resonance, and two novel biochemical 
assays, we demonstrate that CHD5-PHD(1-2) simultaneously engages two H3 
N-termini and results in a 4-11-fold increase in affinity compared with either 
PHD finger alone. These studies provide biochemical evidence for the utility of 
tandem PHD fingers to recruit protein complexes at targeted genomic loci and 
provide the framework for understanding how multiple chromatin-binding modules 
function to interpret the combinatorial PTM capacity written in chromatin.