The study investigates the effects of ATP and other nucleotides, as well as calcium (Ca2+), on the conformational changes in histone H1, a key component of chromatin. Using circular dichroism (CD) spectroscopy, the researchers found that ATP and nucleotides induce a significant increase in the α-helicity of H1, suggesting structural changes in the protein. These changes are accompanied by alterations in H1's interaction with DNA, particularly in AT-rich regions. The presence of Ca2+ also influences H1's conformation, with ATP and Ca2+ together producing a more pronounced effect. The study highlights the importance of nucleotide and Ca2+ binding in H1-mediated chromatin remodeling, providing insights into the mechanisms underlying gene expression regulation.The study investigates the effects of ATP and other nucleotides, as well as calcium (Ca2+), on the conformational changes in histone H1, a key component of chromatin. Using circular dichroism (CD) spectroscopy, the researchers found that ATP and nucleotides induce a significant increase in the α-helicity of H1, suggesting structural changes in the protein. These changes are accompanied by alterations in H1's interaction with DNA, particularly in AT-rich regions. The presence of Ca2+ also influences H1's conformation, with ATP and Ca2+ together producing a more pronounced effect. The study highlights the importance of nucleotide and Ca2+ binding in H1-mediated chromatin remodeling, providing insights into the mechanisms underlying gene expression regulation.