Nucleotide Recognition by Histone H1 Involves Specific Protein Structures

We have reported previously that histone H1 is capable of binding nucleotides such as ATP, GTP, ADP, and GDP in a specific manner. It is demonstrated here using labeling with the uv-crosslinkable ATP analog 8-azido-[α-32P]ATP that this ability is a unique characteristic of H1 among the histone proteins. Phosphate analogs such as AlF−4 efficiently counteract the labeling of H1, while they do not compete for labeling of histones H2A, H2B, H3, and H4. Consistent with the assumption that this labeling is due to specific binding, nucleotides competed for the labeling of H1 in a manner similar to labeling of the catalytic subunit of cAMP-dependent protein kinase, casein kinase-II, and heat shock protein-90, all of which are ATP/GTP-binding proteins. The site of nucleotide interaction was subsequently located in a Gly-rich region of H1 which displays homology with the protein kinases, using either radioactive labeling with nucleotide analogs and endoproteinase Glu-C digestion or synthetic peptides corresponding to the putative binding site. The results imply that specific protein structures are involved in nucleotide binding to H1 and that the ability of H1 to bind nucleotides may provide a mechanism for the regulation of eukaryotic gene expression.