H1-5 binds to linker DNA between nucleosomes, forming the macromolecular structure known as the chromatin fibre. Linker histones of the H1 type are necessary for the condensation of nucleosome chains into higher-order structured fibres, and they promote formation of the H3K27me3 mark by the PRC2/EED-EZH2 complex. H1-5 also acts as a regulator of individual gene transcription through chromatin remodelling, nucleosome spacing and DNA methylation.

Histones are basic nuclear proteins responsible for the nucleosome structure of the eukaryotic chromosomal fibre. Two molecules each of the core histones H2A, H2B, H3 and H4 form an octamer, around which approximately 146 bp of DNA is wrapped in repeating nucleosome units. The linker histone H1 sits outside this core particle, interacting with the linker DNA and compacting chromatin. H1-5 belongs to the histone H1/H5 family and is found in the nucleus, associated with chromosomes. The H1-5 protein is encoded by an intronless gene that produces a replication-dependent histone. Its transcripts lack polyA tails and instead contain a palindromic termination element. The H1-5 gene lies in the small histone gene cluster on chromosome 6p22-p21.3.

The gene has been listed under several names, including H1 histone family, member 5; histone 1, H1b; histone cluster 1, H1b; and histone cluster 1 H1 family member b, giving the symbols HIST1H1B, H1F5, H1b and H1s-3. HGNC places it in the H1 histones gene group, and mouse and rat each have an ortholog named H1-5.