Human tNASP Promotes in Vitro Nucleosome Assembly
with Histone H3.3
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Abstract
Nuclear
autoantigenic sperm proteins (NASPs) are members of the
acidic histone chaperones, which promote nucleosome assembly. In humans,
two splicing variants proposed for the somatic and testicular isoforms,
sNASP and tNASP, respectively, have been found, and the shorter form,
sNASP, reportedly promotes nucleosome assembly with the histone H3
isoforms, H3.1, H3.2, and H3.3. However, the biochemical properties
of the longer form, tNASP, have not been reported. tNASP is considered
to exist specifically in the testis. Our present results revealed
that the tNASP protein is ubiquitously produced in various human tissues,
in addition to testis. Unexpectedly, we found that the nucleosome
assembly activity of purified tNASP was extremely low with the canonical
histone H3.1 or H3.2, but was substantially detected with the replacement
histone H3.3 variant. A mutational analysis revealed that the H3.3
Ile89 residue, corresponding to the H3.1 Val89 residue, is responsible
for the tNASP-mediated nucleosome assembly with H3.3. A histone deposition
assay showed that the H3.3–H4 complex is more efficiently deposited
onto DNA by tNASP than the H3.1–H4 complex. These results provide
evidence that tNASP is ubiquitously produced in various types of human
tissues and promotes in vitro nucleosome assembly with H3 variant
specificity