Histone acetylation readers Bdf1 and Yaf9 guide targeting of SWR1 remodeler  to +1 nucleosome
The histone variant H2A.Z marking permissive chromatin is preferentially deposited at promoter-proximal +1 nucleosomes by the multicomponent SWR1 chromatin remodeler. Although SWR1 targeting to nucleosome-depleted regions (NDRs) is directed by its free DNA length sensing module, how the remodeler is guided preferentially to flanking +1 nucleosomes has been enigmatic. Here, we show by live-cell, single-molecule tracking (SMT) that SWR1 subunits Bdf1 and Yaf9 harboring bromo and YEATS acetyl-histone reader domains are required for quantitative chromatin binding via distinct kinetic mechanisms: Bdf1 increases SWR1 association, Yaf9-YEATS reduces disassociation.  Notably, SMT and genome-wide ChIP-exo reveals Bdf1 and Yaf9 contributions to SWR1 targeting globally and histone exchange at +1 nucleosomes. Our findings highlight the native biochemistry of histone readers and suggest a broadly applicable, two-stage mechanism wherein acetyl-histone interactions initially constrain 3D diffusion of SWR1 to increase local concentration, followed by stochastic 1D diffusion at NDRs with directional capture by acetylated +1 nucleosomes. Overall design: Chromatin Immunoprecipitation DNA-sequencing with exonuclease treatment (ChIP-exo) for histone variant H2A.Z and chromatin remodeler Swr1 in S. Cerevisiae with genetic modifications in the SWR1 complex