Studies on the interaction of H1 histone with superhelical DNA: Characterization of the recognition and binding regions of H1 histone

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Abstract
Fhe very 1.vsine rich histone. H1. isolated from a variety of sources interactfgpkfekt ially with superhelical DNA compared to relaxed DNA duplexes . The nature of this specific i nteraction has been investi- gated by studying the ability of various purified fragments of H1 histone from calf thymus to recognize and bind superhelical DNA. The data suggest that the globular region of the H1 histone molecule (amino acid residues 72-106) is involved in the recognition of superhelical DNA. Thus, the H1 histone carboxy-terminal fragment, 72-212, resembles native H1 histone both quantitatively and qualitatively in its ability to discriminate between and bind to superhelical and relaxed DNA while the H1 histone carboxy-terminal fragment, residues 106-212, has lost this specificity, binding superhelical and relaxed DNA equally well. Furthermore, under conditions in which the lobular region of the intact H1 histone has been unfolded, the molecule 9 oses its ability to discriminate between superhelical and relaxed DNA, and binds both forms of DNA equally.