The linker histone that binds DNA between nucleosomes is histone H1. Unlike the four core histones that form the nucleosome’s central octamer, H1 associates with DNA near the nucleosome’s entry and exit points and with the adjoining linker DNA.
This positioning lets H1 act like a clamp or architectural brace. It helps stabilize the DNA wrapped around the core particle and promotes tighter organization of nucleosome arrays into more compact chromatin. H1 does not replace H2A, H2B, H3, or H4; those proteins make up the core octamer itself.
A common mix-up is treating “linker histone” as one completely uniform protein. H1 is better understood as a family of related proteins. Mammals have multiple H1 variants, with some expressed during DNA replication and others associated with particular tissues or developmental stages. Their shared role is broad chromatin organization, although individual variants can have distinct effects.
The linker DNA length varies among organisms and cell types. This variability means H1 helps organize chromatin without imposing one identical spacing pattern throughout every genome.