[Nucleomeric organization of chromatin]

Area of Science:

• * Molecular Biology: Investigating the higher-order structure of chromatin.
• * Biochemistry: Analyzing the role of divalent cations and histone proteins in chromatin organization.

Context:

• * Chromatin, the complex of DNA and proteins in eukaryotic nuclei, exists in various structural states.
• * The globular nucleomeric fibril, 20-25 nm in diameter, represents a key organizational unit of fixed and isolated chromatin.

Purpose:

• * To elucidate the structural organization of chromatin at the nucleomer level.
• * To investigate the role of Mg2+ and histone H1 in nucleomer structure and dynamics.
• * To propose a model for nucleomer fibril structure and its functional implications.

Summary:

• * Chromatin fibrils are composed of globular nucleomers (20-25 nm) that can be fragmented by nucleases.
• * Nucleomers unfold into nucleosomal chains upon Mg2+ removal, with structural transitions influenced by histone H1.
• * A model suggests alternating helical organization and impaired bonds within nucleomeric fibrils.

Impact:

• * Understanding nucleomer structure provides insights into DNA accessibility and site-specific recognition.
• * The reversible structural transitions of nucleomers may regulate gene expression.
• * This research contributes to a deeper understanding of chromatin's role in cellular processes.