Histone chaperone Chz1 facilitates the disfavouring property of Spt16 to H2A.Z-containing genes in Saccharomyces cerevisiae

Htz1 (histone 2A Z1) deposition at promoters is involved in the transcriptional activation of quiescent genes. Chz1 [chaperone for Htz1 (or H2A)-H2B dimer] is an Htz1-H2B-specific chaperone that delivers histone H2A.Z that substitutes for H2A. Spt16 (suppressor of Ty) functions in transcription elongation and also possesses a histone chaperone activity. However, the links among Chz1, Htz1 and Spt16 remain unknown. In the present study, we determined the genomic binding profiling of Htz1, Pol II (RNA polymerase II) and Spt16 using ChIP microarray experiments and sequenced nucleosomal DNA using a next-generation sequencing technique in wild-type and chz1-deletion strains of Saccharomyces cerevisiae. The results of the present study revealed that Spt16 and Pol II are associated, bind at nucleosome-depleted regions, and are positively correlated with the transcription rate. Importantly, Spt16 disfavours the Htz1-bound genes, and this discrimination is impaired upon the deletion of chz1. The negative correlation between the binding profiles of Spt16 and Htz1 at promoters is not an intrinsic repulsion, but is probably due to a requirement for transcription initiation. We showed that chz1 deletion decreases Htz1 binding at promoters and telomeres. Also, in the chz1-deletion mutant, Spt16 binding at ribosomal genes was lost. The results of the present study suggest that the discrimination of Spt16 to Htz1-bound genes is due to the priority of Chz1 over Spt16 in binding to the Htz1-bound genomic regions. Chz1-escorted Htz1 therefore impairs Spt16 binding at chromatin.