Dissecting nucleosome function with a comprehensive histone H2A and H2B mutant library

Using a comprehensive library of histone H2A and H2B mutants, we assessed the biological function of each amino acid residue involved in various stress conditions including exposure to different DNA damage-inducing reagents, different growth temperatures, and other chemicals. H2B N- and H2A C-termini were critical for maintaining nucleosome function and mutations in these regions led to pleiotropic phenotypes. Additionally, two screens were performed using this library, monitoring heterochromatin gene silencing and genome stability, to identify residues that could compromise normal function when mutated. Many distinctive regions within the nucleosome were revealed. Furthermore, we used the barcode sequencing (bar-seq) method to profile the mutant composition of many libraries in one high-throughput sequencing experiment, greatly reducing the labor and increasing the capacity. This study not only demonstrates the applications of the versatile histone library, but also reveals many previously unknown functions of histone H2A and H2B.