Nucleosome assembly protein 1 (Nap1) is a histone chaperone implicated in histone regulation through interactions with core histones and linker histone H1, as well as in nucleosome formation and gene regulation. Nap1 is thought to assemble nucleosomes through the prevention of non-nucleosomal histone-DNA interactions in vitro and in vivo . Nap1 is a homo-dimer composed of two 48 kDa polypeptides with disordered N- and C-terminal tails that emerge at the underside of the dome-shaped structure . Preliminary data shows the acidic C-terminal tail is essential for resolving non-nucleosomal histone-DNA interactions. Through affinity measurements in vitro, paired with Electrophoretic Mobility Shift Assays (EMSA), we have determined that the C-terminal tail is required for wild type Nap1 function. We also determined it aids in shielding the inhibitory N-terminal tail. It is unknown whether this mechanism applies to other Nap1-family members such as human Nap1 (hNap1) and SET, and this will be investigated here. It has been shown that Nap1 is primarily a H2A/H2B histone chaperone . Since Nap1 primarily functions with H2A/H2B, our research has focused on determining the mechanism. Using hydrogen-deuterium exchange coupled to Mass Spectrometry (H/DX-MS), our laboratory has recently shown that H2A/H2B rapidly samples a partially unfolded state (S. D'Arcy, submitted). When bound to yeast Nap1 (yNap1), H2A/H2B is then stabilized in a folded conformation (S. D'Arcy, submitted). It is unknown whether DNA will also stabilize H2A/H2B in a folded conformation like yNap1 does. Likewise, does yNap1 also stabilize the folded state of linker histone H1? Through the use of H/DX we will be able to answer these questions. Since H/DX is only a medium resolution technique, we can only gather information on tertiary structure. To obtain greater resolution, x-ray crystallography will used. It will provide great detail of the molecular interactions that can enhance our knowledge of the role that histone chaperones have in nucleosome dynamics.