A DNA-binding homeodomain in histone H1

DNA binding of histone H1 is modulated by nucleotides

Histone H1 acts as a general repressor of transcription in eukaryotes by organizing nucleosomes into inaccessible condensed forms of chromatin. The capability of H1 to bind to DNA with some sequence specificity is likely to be critical in the control of these processes. We show here that ATP and several other nucleotides, including non-hydrolyzable derivatives, can inhibit DNA binding of H1. The results also show that ATP differentially affects binding of H1 to DNA in a fashion enhancing nucleotide sequence specificity of the binding. The study suggests a novel mechanism of modulation of H1 activity that has important implications for the role of H1 as a transcriptional regulator.

Site-directed mutagenesis studies on the binding of the globular domain of linker histone H5 to the nucleosome

The globular domain of the linker histone H5 has been expressed in Escherichia coli. The purified peptide is functional as it permits chromatosome protection during micrococcal nuclease digestion of chromatin reconstituted with the peptide, indicating that it binds correctly at the dyad axis of the nucleosomal core particle. The globular domain residue lysine 64 is highly conserved within the linker histone family, and site-directed mutagenesis has been used to assess the importance of this residue in the binding of the globular domain of linker histone H5 to the nucleosome. Recombinant peptides mutated at lysine 64 are unable to elicit chromatosome protection to the same degree as the wild-type peptide, and since they appear to be fully folded, these observations confirm a major role for this residue in determining the effective interaction between the globular domain of histone H5 and the nucleosome.

A model for histone H5-DNA interaction: simultaneous minor and major groove binding

Using the tertiary structure of the globular domain of H5 (GH5) and based on an alternative sequence homology between GH5 and DNA-binding proteins containing the helix-turn-helix motif, a model for H5-DNA interaction is proposed. From molecular graphics it follows that helix II recognizes the major groove of the DNA, as does the second helix of the helix-turn-helix motif, while helix III makes minor groove contacts, in agreement with the hypothesis of Turnell et al. (FEBS letters 232, 263-268). In the resulting model GH5 makes contact with a full turn of DNA.

The predicted molecular structure suggests that CTF/NF-I may function as a histone acetylase

The primary structure of nuclear factor-I (CTF/NF-I), a eukaryotic regulatory DNA-binding protein involved in both DNA replication and gene transcription, and the secondary structure predictable from it, are compared here with those of a number of prokaryotic acetylases. Hydropathy and Chou-Fasman analyses reveal that the polypeptide chain of CTF/NF-I is likely to fold to higher order structures similar to those of the acetylases, and significant conservation of functionally important regions of the acetylases is observed in CTF/NF-I. It is therefore suggested that CTF/NF-I may function as a histone acetylase.