A novel role for Nhp6 proteins in histone gene regulation in Saccharomyces cerevisiae

Maintaining a stable and balanced histone pool is of paramount importance for genome stability and fine regulation of DNA replication and transcription. This involves a complex regulatory machinery, exploiting transcription factors as well as histone chaperones, chromatin remodelers and modifiers. The functional details of this machinery are as yet unclear. Previous studies report histone decrease in mammalian and yeast HMGB family mutants. In this study we find that Nhp6 proteins, the S. cerevisiae HMGB1 homologues, control histone gene expression by affecting nucleosome stability at regulative regions of the histone clusters. In addition, we observe that histone gene overexpression in the nhp6ab mutant is accompanied by downregulated translation, which in turn is responsible for the histone decrease phenotype. Our observations allow us to incorporate Nhp6 proteins into the large group of chromatin factors that tightly regulate histone gene expression.