Co-operative interactions of oligonucleosomal DNA with the H1e histone variants and its poly (ADP-ribosyl)ated isoforms

H1 histone somatic variants from L929 mouse fibroblasts were purified by reverse-phase HPLC. We analysed the ability of each H1 histone variant to allow the H1–H1 interactions that are essential for the formation of the higher levels of chromatin structure, and we investigated the role played by the poly(ADP-ribosyl)ation process. Cross-linking analysis showed that H1e is the only somatic variant which, when bound to DNA, is able to produce H1–H1 polymers; the size of polymers was decreased when H1e was enriched in its poly(ADP-ribosyl)ated isoform. Measurement of the methyl-accepting ability in native nuclei compared with nuclei in which poly(ADP-ribosyl)ation was induced showed that the poly(ADP-ribosyl)ated H1 histone had not been removed from linker regions, in spite of its different interaction with DNA.