Nucleosome Assembly by the Chaperonosome: Complex of a Chaperone-Bound Histone Octamer

At any time in the nucleus of a eukaryotic cell, chromatin, the protein-DNA supercomplex that harbors the genome, undergoes various processes to meet the needs of the cell during its life cycle. These processes serve to regulate the replication, transcription, or repair of the DNA and are as such dependent on the dynamics of the nucleosome, the fundamental repeating unit of chromatin. A nucleosome is assembled from a protein core of histone proteins around which DNA is wrapped. However, for nuclear processes in which the DNA serves as template for proteins, DNA has to be (partially) unwrapped in a process called nucleosome disassembly. Nucleosome assembly and disassembly are dependent on a family of proteins called histone chaperones. These chaperones bind and manage the histone proteins for all chromatin processes. One of these processes is repair of DNA double-strand breaks (DSBs), a common type of DNA damage in eukaryotic cells. The major pathway for DSB repair in human cells is non-homologous end joining (NHEJ). The NHEJ DNA repair factor Aprataxin and Polynucleotide kinase Like Factor (APLF) was shown to harbor histone chaperone function in its C-terminal acidic domain (APLFAD). The topic of this dissertation is the characterization of the histone chaperone function of APLFAD. A multidisciplinary approach is used to better understand how this histone chaperone functions, from histone binding to nucleosome assembly. The aim is to provide a better understanding of NHEJ DNA repair and the mechanism of nucleosome assembly.