Binding of antibodies against histone H1 to unfolded and folded nucleofilaments

Rabbit antibodies to calf thymus histone H1 were purified by affinity chromatography on histone-H1--Sepharose and used as a probe for detecting histone H1 in the nucleofilaments prepared from rat liver nuclei. Binding of the antibodies to the unfolded form of nucleofilaments in 5 mM NaC1 and to the folded form in 80 mM NaC1 Was compared. Sucrose density gradient analyses clearly show that the antibodies can preferentially bind to nucleofilaments in 5 mM NaC1 but not in 80 mM NaC1. The antibodies, however, can bind to mononucleosomes in 80 mM NaC1. These results suggest that antigenic determinants of histone H1 in unfolded nucleofilaments and in mononucleosomes are accessible to the antibodies, while those in folded nucleofilaments are not. This is consistent with the view that histone H1 is used for folding and packing of a nucleosomal chain.