Histone H3 is one of the core components of the nucleosome. The nucleosome is the smallest subunit of chromatin and consists of 146 base pairs of DNA wrapped around an octamer of core histone proteins (two each of H2A, H2B, H3 and H4). Histone H1 is a linker protein, present at the interface between the nucleosome core and DNA entry/exit points. Nuclear core histone H3 exist as several variants: H3.1, H3.2, H3.3, CENP-A and H3t. These variants have been suggested to have specific functions in the regulation of gene expression and genome stability. H3.1t, also called as H3T or H3.4, is a variant of histone H3 that is robustly expressed in the human testis. Like the conventional H3.1, H3.1t can be assembled into nucleosomes with H2A, H2B, and H4 (H3T nucleosome). A histone chaperone, Nap2 was found to be a more efficient chaperone for H3T nucleosome assembly than the ubiquitously expressed histone chaperone, Nap1. Therefore, H3.1t may be assembled into the chromatin by a specific chaperone-mediated pathway in the testis.
