Use of protein blotting to study the DNA-binding properties of histone H1 and H1 variants

Sub-types of histone H1 have been observed in a variety of tissues from several organisms. One of the best characterized H1 variants is H5 from avian erythrocytes. Several lines of evidence suggest that H5 has a greater affinity for DNA than H1 and is thus thought to account, in part, for the highly condensed and transcriptionally repressed state of avian erythrocyte chromatin. In trout there is an analogous erythrocyte-specific H1 variant, previously termed 'H5' [B.L.A. Miki and J.M. Neelin (1975) Can. J. Biochem. 53, 1158-1169). Using a sensitive and rapid protein-blotting procedure which is specific amongst the histones for histone H1 and its variants, we compared DNA-binding properties of the trout erythrocyte histone 'H5' and chicken H5. By increasing the NaCl concentration of the binding buffer, a gradual decrease in the amount of DNA that bound to chicken H1, trout H1 and trout erythrocyte 'H5' variant was observed, such that at concentrations above 0.37 M, negligible amounts of DNA were bound. By contrast, chicken H5 bound a significantly greater amount of DNA even at a concentration of 0.4 M NaCl. Based on the DNA-binding, properties, we conclude that the trout erythrocyte variant 'H5' is more closely related to H1 than to H5. By assaying the DNA-binding affinity of calf thymus H1 DNA-binding affinity of calf thymus H1 peptide fragments, generated by protease and chemical cleavage, and the sperm-specific H1 variants of the annelid, Platynereis dumerilii, which possess greatly shortened C-terminal tails, we conclude that a domain that includes a very small portion of the C-terminal tail and part of the globular domain is sufficient for the binding of H1 to DNA.