Structure and dynamics of the yeast SWR1-nucleosome complex.

The yeast SWR1 complex exchanges histone H2A in nucleosomes with Htz1 (H2A.Z in humans). The cryo-electron microscopy structure of the SWR1 complex bound to a nucleosome at 3.6-angstrom resolution reveals details of the intricate interactions between components of the SWR1 complex and its nucleosome substrate. Interactions between the Swr1 motor domains and the DNA wrap at superhelical location 2 distort the DNA, causing a bulge with concomitant translocation of the DNA by one base pair, coupled to conformational changes of the histone core. Furthermore, partial unwrapping of the DNA from the histone core takes place upon binding of nucleosomes to SWR1 complex. The unwrapping, as monitored by single-molecule data, is stabilized and has its dynamics altered by adenosine triphosphate binding but does not require hydrolysis.