nucleoidként

The nucleoid is the irregular, non-membrane-bound region within prokaryotic cells where the cell’s genetic material resides. It contains the main chromosome, typically a circular DNA molecule, and often additional genetic elements such as plasmids. While many bacteria carry a single chromosome, some species harbor multiple replicons, and archaeal genomes can display a variety of organizational features.

DNA in the nucleoid is densely packed through supercoiling, DNA-binding proteins, and macromolecular crowding. Nucleoid-associated proteins, including HU, IHF, FIS, and H-NS in bacteria, help shape the DNA into looping domains and regulate access by RNA polymerase. In archaea, histone-like proteins contribute to a similar compaction and organization. Topoisomerases, such as DNA gyrase and topo I, modulate supercoiling during replication and transcription, enabling dynamic remodeling of the nucleoid.

Nucleoid structure is dynamic and responsive to growth conditions, stress, and cell-cycle stage. Some bacteria exhibit macrodomains—larger, functionally distinct DNA regions that influence recombination and gene expression. The activities of transcription and replication continually reshape nucleoid organization, while changes in DNA density can feedback to affect gene accessibility.

Compared with a eukaryotic nucleus, the nucleoid lacks a surrounding membrane and defined subcompartments. Its organization is fluid and constantly remodeled to balance genome compaction, replication, repair, and transcription. Understanding nucleoids illuminates how prokaryotes fit large genomes into small cells and regulate gene expression in changing environments.