Histones H1 are necessary for the condensation of nucleosome chains into higher-order structures. Interacts with RRP1B. Expressed ubiquitously. Citrullination at Arg-62 (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.