Histone H1 acts on the linker region of polynucleosome DNA to condense the chromatin into structures of ~30 nm (1). It is not necessary for octamer or nucleosome core particle formation. Eight different Histone H1 proteins have been identified in the human genome (2). Histone H10 is a non replication-dependent histone that is highly expressed in cells that have terminally differentiated (3).