Molecular characteristics of porcine thymus histone H1 variants

We constructed an assay system to measure the annealing activity that is one of the functional features of nuclear proteins, using ssDNAs derived from M13 phage recombinants which contained a complementary 406-bp portion each. Histone H1 variants were purified from porcine thymus by separation of chromatin, extraction with 5% perchloric acid, and reversed-phase HPLC. Three types of histone H1 variants were found by analysis of amino acid composition and on SDS-PAGE. All of these could promote the annealing. According to Hill's analysis all had similar numbers of binding sites to DNA strands but dissociation constants and annealing activity were different. The number of binding sites, dissociation constants, and annealing activity were changed by dephosphorylation of histone H1 variants. This result suggests that histone H1 variants have different affinities for DNA molecules and ssDNA-annealing activity, which is regulated by phosphorylation.