Histone H1 (H1)

Histone H1 is one of the 5 main histone protein families which are components of chromatin in eukaryotic cells, and is the most variable histone in sequence across species. A variant of the histone H1 protein is the histone H5, which has a similar structure and function, but is only found in avian erythrocytes, which unlike mammalian erythrocytes, have nuclei.Featuring a central globular domain and long C- and N-terminal tails, H1 is involved with the packing of the "beads on a string" sub-structures into a high order structure, whose details have not yet been solved.

H1 is present in half the amount of the other four histones. This is because unlike the other histones, H1 does not make up the nucleosome "bead". Instead, it sits on top of the structure, keeping in place the DNA that has wrapped around the nucleosome.