Histone H1 protein binds to linker DNA between nucleosomes forming the macromolecular structure known as the chromatin fiber. Histones H1 are necessary for the condensation of nucleosome chains into higher-order structured fibers. Acts also as a regulator of individual gene transcription through chromatin remodeling, nucleosome spacing and DNA methylation (By similarity). Interacts with DFFB. Mainly localizes in euchromatin. The C-terminal domain is required for high-affinity binding to chromatin. H1 histones are progressively phosphorylated during the cell cycle, becoming maximally phosphorylated during late G2 phase and M phase, and being dephosphorylated sharply thereafter. Citrullination at Arg-57 (H1R54ci) by PADI4 takes place within the DNA-binding site of H1 and results in its displacement from chromatin and global chromatin decondensation, thereby promoting pluripotency and stem cell maintenance. Belongs to the histone H1/H5 family.