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#SWI/SNF

2 public questions tagged with this topic.

Regulation of chromatin structure

Which complex mediates sliding of nucleosomes along DNA?

ATP-dependent remodeling complexes reorganize chromatin by mobilizing nucleosomes without covalent modification. SWI/SNF family members contain Brg1 or Brm ATPase subunits that translocate DNA relative to octamer, peeling off contacts at entry site and propagating bulge around particle to shift position along duplex. Sliding exposes previously occluded transcription factor binding sites, facilitates activator binding and promoter clearance. Unlike ISWI which spaces nucleosomes regularly, SWI/SNF generates disordered arrays and ejects octamers at high density, acting as transcriptional co-activator at inducible genes requiring rapid access during development and stress response.

Ref: Clapier and Cairns, Annu Rev Biochem 2009: SWI/SNF Complex Mediates Nucleosome Sliding Mechanism

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Regulation of chromatin structure

Which nucleosome remodeling complex contains a DNA translocase?

Chromatin remodeling complexes use ATP hydrolysis to translocate along DNA and alter histone-DNA contacts. Core subunits contain Snf2-like superfamily 2 helicase translocase domains with ATPase activity, coupled to DNA binding and directionally pumping DNA around octamer. In SWI/SNF, ISWI, CHD and INO80 families, the translocase pulls DNA from linker region, generating torsional strain, transient loop or bulge propagation, resulting in sliding or ejection. This DNA translocase activity is distinct from HAT or methyltransferase chemistry and underlies nucleosome repositioning, exposing regulatory sequences to transcription factors and polymerases.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 9: ATP-Dependent Chromatin Remodeling Complexes Contain DNA Translocase

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