Which histone is linker histone?
Nucleosome core contains four canonical histones H2A, H2B, H3, H4 forming octamer wrapping 147 base pairs. H1 differs structurally and functionally as fifth histone. Called linker histone, it does not integrate inside octamer but binds at dyad where DNA enters and exits nucleosome, protecting additional twenty base pairs to generate chromatosome of 167 base pairs. Its central winged-helix globular domain plus long lysine-rich C-terminal tail neutralizes linker DNA, facilitates folding of beads-on-string 11 nanometer fiber into 30 nanometer fiber and stabilizes higher-order condensation during
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 4: Nucleosome Core and Linker Histone H1 Binding
