The impact of the HIRA histone chaperone upon global nucleosome architecture

HIRA is an evolutionarily conserved histone chaperone that mediatesreplication-independent nucleosome assembly and is important for a variety of processessuch as cell cycle progression, development, and senescence. Here we have used a chromatinsequencing approach to determine the genome-wide contribution of HIRA to nucleosomeorganization in Schizosaccharomyces pombe. Cells lacking HIRA experiencea global reduction in nucleosome occupancy at gene sequences, consistent with the proposedrole for HIRA in chromatin reassembly behind elongating RNA polymerase II. In addition, wefind that at its target promoters, HIRA commonly maintains the full occupancy of the−1 nucleosome. HIRA does not affect global chromatin structure at replicationorigins or in rDNA repeats but is required for nucleosome occupancy in silent regions ofthe genome. Nucleosome organization associated with the heterochromatic(dg-dh) repeats located at the centromere is perturbed by loss of HIRAfunction and furthermore HIRA is required for normal nucleosome occupancy at Tf2 LTRretrotransposons. Overall, our data indicate that HIRA plays an important role inmaintaining nucleosome architecture at both euchromatic and heterochromatic loci.