The multifunctional protein nucleophosmin (NPM1) is a human linker histone H1 chaperone.

Linker histone H1plays an essential role in chromatinorganization. Proper deposition of linker histone H1as well as its removal is essential for chromatindynamics and function. Linker histonechaperones perform this important task during chromatinassembly and other DNA-templated phenomena in the cell. Our in vitro data show that the multifunctional histonechaperone NPM1interacts with linker histone H1through its first acidic stretch (residues 120−132). Association of NPM1with linker histone H1was also observed in cells in culture. NPM1exhibited remarkable linker histone H1chaperone activity, as it was able to efficiently deposit histone H1onto dinucleosomal templates. Overexpression of NPM1reduced the histone H1occupancy on the chromatinizedtemplate of HIV-1 LTR in TZM-bl cells, which led to enhanced Tat-mediated transactivation. These data identify NPM1as an important member of the linker histonechaperone family in humans.