Histone H1 protein binds to linker DNA between nucleosomes forming the macromolecular structure known as the chromatin fiber (By similarity). Histones H1 are necessary for the condensation of nucleosome chains into higher-order structured fibers and promote formation of the H3K27me3 mark by the PRC2/EED-EZH2 complex (PubMed:40516528). Also acts as a regulator of individual gene transcription through chromatin remodeling, nucleosome spacing and DNA methylation (By similarity). {ECO:0000250|UniProtKB:P10412, ECO:0000269|PubMed:40516528}. This is the function of H1-5 (H1.5 linker histone, cluster member, Ensembl gene identifier ENSG00000184357).