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Related publication: Willhoft O., Ghoneim M., Lin C.-L., Chua E.Y.D., Wilkinson M., Chaban Y., Ayala R., McCormack E.A., Ocloo L., Rueda D.S., & Wigley D.B. Structure and dynamics of the yeast SWR1-nucleosome complex. Science (80-. ). 362, eaat7716 (2018). DOI: 10.1126/ science.aat7716
The work recently published in the journal Science by a team of scientists from Imperial College London featured the structure of the SWR1:nucleosome complex at 3.6 Å resolution, determined using cryo-Electron Microscopy (cryo-EM) data collected at the UK national electron Bio-Imaging Centre (eBIC).
The “Histone Code” theory, proposed at the turn of the century, stated that coordinated patterns of modifications to DNA-packaging histones may be a key factor in turning specific genes on or off1. Currently, two distinct classes of chromatin alterations are identified, and usually performed by different types of enzymes: 1) chemical modification of histone tails, and 2) active modification of chromatin structure, or chromatin remodelling. Both processes appear to be interlinked and tightly controlled throughout the cell cycle. Deregulation of these processes results in abnormalities in gene expression patterns that can lead to significant changes in cell chemistry, and subsequent tissue degeneration, or cancer. Yeast SWR1 complex (related to SRCAP and Tip60 complexes in human) mediates the incorporation of conserved Htz1 variant of H2A histone into chromatin. Htz1 has been implicated in transcriptional regulation, and prevention of the spread of the condensed form of chromatin, heterochromatin2.
The Swc6 subunit of the complex is seen interacting with DNA on the opposite side to the Swr1 ATPase motor domain. DNA is unwrapped from the canonical nucleosome path, exposing 2.5 turns of the wrap. A single alpha helix of Swc6 interacts with the surface of H2A histone (Fig. 2). The interaction site involves histone residues which differ between H2A and Htz1, and thus may contribute to enzyme specificity.
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