Stepwise histone replacement by SWR1 requires dual activation with histone H2A.Z and canonical nucleosome.
Histone variant H2A.Z-containing nucleosomes are incorporated at most eukaryotic promoters. This incorporation is mediated by the conserved SWR1 complex, which replaces histone H2A in canonical nucleosomes with H2A.Z in an ATP-dependent manner. Here, we show that promoter-proximal nucleosomes are highly heterogeneous for H2A.Z in Saccharomyces cerevisiae, with substantial representation of nucleosomes containing one, two, or zero H2A.Z molecules. SWR1-catalyzed H2A.Z replacement in vitro occurs in a stepwise and unidirectional fashion, one H2A.Z-H2B dimer at a time, producing heterotypic nucleosomes as intermediates and homotypic H2A.Z nucleosomes as end products. The ATPase activity of SWR1 is specifically stimulated by H2A-containing nucleosomes without ensuing histone H2A eviction. Remarkably, further addition of free H2A.Z-H2B dimer leads to hyperstimulation of ATPase activity, eviction of nucleosomal H2A-H2B, and deposition of H2A.Z-H2B. These results suggest that the combination of H2A-containing nucleosome and free H2A.Z-H2B dimer acting as both effector and substrate for SWR1 governs the specificity and outcome of the replacement reaction.
Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. luked@mail.nih.gov
Ed
E
Luk
Anand
A
Ranjan
Peter C
PC
Fitzgerald
Gaku
G
Mizuguchi
Yingzi
Y
Huang
Debbie
D
Wei
Carl
C
Wu
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D042002:Chromatin Assembly and Disassembly; D019281:Dimerization; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D006657:Histones; D009707:Nucleosomes; D029701:Saccharomyces cerevisiae Proteins; D000251:Adenosine Triphosphatases; C481261:Swr1 protein, S cerevisiae