Some assembly required: structural and mechanistic studies of histone chaperones, nucleosome assembly factors and ATP dependent chromatin remodelers.

All eukaryotes organize their DNA into nucleosomes, consisting of an octamer of the four core histone proteins H2A, H2B, H3, and H4, around which 147 base pairs of DNA are wrapped in two tight superhelical turns. Nucleosomes pack into higher order structures and require histone chaperones and ATP-dependent remodelers to make the DNA accessible. I will discuss our recent progress in understanding the higher order structure of chromatin at the centromere, and the role of centromere-binding proteins in locally folding the chromatin fiber. I will also discuss mechanisms by which nucleosomes are remodeled and assembled in an ATP dependent and ATP-independent manner. The histone chaperone FACT binds and stabilizes partially disassembled nucleosomes by employing an acidic C-terminal domain as a DNA mimic to clamp down a histone dimer. The chromatin remodeler SMARCAD1 requires ATP hydrolysis to remove histones from a nucleosome, which it then can deposit onto a new DNA segment in an ATP-independent mechanism, and I will present biochemical and structural evidence for this mode of action.