Abstract
SummaryThe ATP-dependent chromatin-remodeling complex SWR1 exchanges a variant histone H2A.Z/H2B dimer for a canonical H2A/H2B dimer at nucleosomes flanking histone-depleted regions, such as promoters. This localization of H2A.Z is conserved throughout eukaryotes. SWR1 is a 1 megadalton complex containing 14 different polypeptides, including the AAA+ ATPases Rvb1 and Rvb2. Using electron microscopy, we obtained the three-dimensional structure of SWR1 and mapped its major functional components. Our data show that SWR1 contains a single heterohexameric Rvb1/Rvb2 ring that, together with the catalytic subunit Swr1, brackets two independently assembled multisubunit modules. We also show that SWR1 undergoes a large conformational change upon engaging a limited region of the nucleosome core particle. Our work suggests an important structural role for the Rvbs and a distinct substrate-handling mode by SWR1, thereby providing a structural framework for understanding the complex dimer-exchange reaction.
Highlights
Inside the nucleus, eukaryotic DNA condenses into chromatin by associating with evolutionarily conserved histone proteins H2A, H2B, H3, and H4
We obtained the three-dimensional structure of SWR1 and mapped its major functional components
Our data show that SWR1 contains a single heterohexameric Rvb1/Rvb2 ring that, together with the catalytic subunit Swr1, brackets two independently assembled multisubunit modules
Summary
Eukaryotic DNA condenses into chromatin by associating with evolutionarily conserved histone proteins H2A, H2B, H3, and H4. Essential nuclear activities are regulated by processes that target the nucleosome. These processes are best characterized at gene promoters, where the biophysical properties, position, and composition of nucleosomes are strictly regulated. This results in a stereotypical chromatin structure that includes a histone-depleted region flanked by labile yet well-positioned nucleosomes containing the evolutionarily conserved histone variant H2A.Z (Albert et al, 2007; Raisner et al, 2005; Tolstorukov et al, 2009). ATP-dependent chromatin remodeling complexes (remodelers) play a significant role in the regulation of promoter chromatin (Badis et al, 2008; Hartley and Madhani, 2009; Zhang et al, 2011)
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