The histone H3-H4 tetramer is a copper reductase enzyme

We sought to examine whether nucleosomes participate in cellular copper homeostasis by directly catalyzing the reduction of copper, thereby producing the biousable cuprous ion. To test this hypothesis, we disrupted a potential copper coordination site of the nucleosome by mutating the histone H3 His113 residue to an asparagine (H113N) in the budding yeast. We observed that copper homeostasis was indeed perturbed in the H113N mutant. However, given the known roles of nucleosomes in regulating gene expression, it was reasonable to expect that the perturbation of copper homeostasis was due simply to a conincidental disrutpion of the tanscriptional regulation of genes important for copper metabolism. We performed polyA+ RNA sequencing of WT and H3H113N yeast strains in various conditions to assess whether gene expression alterations could account for the copper-related phenotypes. S. cerevisiae strains with or without the H3H113N mutation, and alone or in combination with CTR1 or CCS1 deletions, were grown in various liquid media conditions that tested their ability for proper copper utilization. The H3H113N mutation resulted in copper-dependent growth defects in several of the conditions. Total RNAs were extracted from these cells and subjected to library preparation and Illumina HiSeq sequencing.