![]() ![]() Once deposited, ATP-dependent chromatin remodelers can slide or evict nucleosomes to adjust their locations along the DNA ( 13). In particular, histone chaperones guide the ordered assembly of nucleosomes ( 10) which proceeds through the binding of a histone (H3–H4) 2 tetramer to DNA, followed by the association of two H2A–H2B dimers ( 11, 12). To prevent such deleterious interactions, chaperones bind histone proteins throughout their life cycle, from synthesis through nuclear translocation to DNA incorporation ( 5–9). Moreover, being of positive charge, they tend to non-specifically bind DNA ( 5). Under physiological conditions, histones do not form nucleosomes spontaneously and are in fact prone to aggregation. Enzymes that regulate nucleosome incorporation, stability, positioning or occupancy along DNA shape the nucleosome landscape, exerting genome-wide effects on DNA-related processes. Nucleosomes restrict DNA access and by this protect DNA from damage but also form a barrier for processes that use DNA as a template, including gene transcription and DNA replication ( 2–4). At the core of this packaging are nucleosomes, composed of histone octamers wrapped by ∼147 base pairs (bp) of DNA ( 1). Histones are small proteins that package eukaryotic genomes within chromatin. We provide a unified quantitative screen highlighting regulator roles in retaining nucleosome binding during transcription and preserving genomic packaging. They further triggered re-localization of chaperones to affected gene body regions, which compensated for nucleosome loss during transcription complex passage, but concurred with extensive TF binding in gene bodies. Depletion of Spt6, Spt16 or Chd1 sharply increased nucleosome replacement sequentially at the beginning, middle or end of highly expressed gene bodies. ![]() ![]() While replication-independent exchange in unperturbed cells maps to promoters, regulator depletions primarily affected gene bodies. We have recently generated histone-exchange sensors in Saccharomyces cerevisiae, which we now use to define the contributions of 15 regulators to histone dynamics genome-wide. Defining specific in-vivo activities requires monitoring histone dynamics during regulator depletion, which has been technically challenging. Cells express multiple such chromatin regulators with overlapping in-vitro activities. DNA packaging within chromatin depends on histone chaperones and remodelers that form and position nucleosomes. ![]()
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