DNAcondensing

DNAcondensing refers to the set of cellular processes that compact DNA from its extended length into higher-order structures capable of fitting into a cell’s nucleus, while preserving accessibility for essential processes. Condensation is a universal feature of life and is dynamically regulated to balance genome stability, replication, transcription, and segregation.

In eukaryotes, condensation begins with nucleosome formation, where DNA wraps around histone octamers to form a bead-on-a-string fiber. This is followed by further folding into higher-order structures, including loop domains supported by a protein scaffold. During cell division, mitotic chromosomes become highly condensed through the action of condensin and cohesin complexes, with topoisomerases resolving torsional stress and chromatin remodelers adjusting nucleosome positioning. Histone modifications, such as acetylation and methylation, influence compaction by modulating interactions among nucleosomes and chromatin-associated factors, thereby affecting gene accessibility.

In bacteria and archaea, DNA condensation relies on nucleoid-associated proteins and DNA supercoiling to produce a compact nucleoid. Proteins such as HU, H-NS, IHF, and FIS in bacteria help bend and bridge DNA, forming looped domains that organize the genome without a surrounding nucleus.

Other specialized cases include sperm chromatin, where histones are replaced by protamines to achieve extreme compaction, and organellar genomes that require distinct packaging strategies. Disruptions to condensation can impact gene expression, genome stability, and cell division. Studies employ chromosome spreads, advanced microscopy, and chromosome conformation capture techniques to investigate DNAcondensing.