sNASP, a histone H1-specific eukaryotic chaperone dimer that facilitates chromatin assembly

¹ Dept. of Biochemistry & Microbiology, University of Victoria

^* To whom correspondence should be addressed. E-mail: jausio{at}uvic.ca.

Submitted on January 22, 2008
Revised on March 20, 2008
Accepted on 3 April 2008

	Abstract

Nuclear autoantigenic sperm protein (NASP) has been described as a histone H1 chaperone in mammals. However, the molecular mechanisms involved have not yet been characterized. Here, we show that this protein is not only present in mammals but it is widely distributed throughout eukaryotes both in its somatic (sNASP) and testicular (tNASP) forms. The secondary structure of the human somatic version consists mainly of clusters of -helices and exists as a homodimer in solution. The protein binds non-specifically to core histone H2A-H2B dimers and H3-H4 tetramers but only forms specific complexes with histone H1.The formation of the NASP-H1 complexes is mediated by the N- and C-terminal domains of histone H1 and it does not involve the winged-helix domain which is characteristic of linker histones. In vitro chromatin reconstitution experiments show that this protein facilitates the incorporation of linker histones onto nucleosome arrays and hence is a bona fide linker histone chaperone.

Key Words: chaperone, chromatin, circular dichroism, histone H1, nuclear autoantigenic sperm protein, sedimentation velocity