Which nucleosome remodeling action removes H2A-H2B dimers?
Nucleosome remodeling encompasses sliding, ejection, dimer exchange and loop formation driven by ATP-dependent complexes. Dimer exchange specifically replaces canonical H2A-H2B dimers with variants like H2A.Z or H2A.X without complete octamer disassembly. SWR1 and INO80 complexes mediate this reaction through ATP-driven distortion of DNA at superhelical location 2, transiently opening dimer-tetramer interface and swapping in variant dimer from chaperone-bound pool. This mechanism establishes specialized chromatin domains at promoters and damage sites, altering nucleosome stability and recruitment of regulatory factors while preserving underlying H3-H4 tetramer.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 9: Chromatin Remodeling Complexes, Dimer Exchange