superkoiling

Superkoiling is a term occasionally used in discussions of DNA topology to describe a state of DNA that is more highly twisted than what is typically observed in vivo. It extends the idea of DNA supercoiling, the over- or under-winding of the double helix, to extreme or pathological levels. The term is not universally adopted and is mostly found in specialized literature or informal usage.

DNA topology involves twist and writhe; supercoiling arises when twist is transferred to the helix, leading to compact structures; superkoiling would involve heightened levels of torsional stress, either positive (over-wound) or negative (under-wound). In cells, the balance is managed by topoisomerases and by forces during replication and transcription.

Enzymes: DNA gyrase (in bacteria) introduces negative supercoils; topoisomerase I and II relieve or redistribute supercoils; in eukaryotes, type I and II topoisomerases perform similar functions; dysregulation can lead to replication fork stalling, DNA damage, chromatin remodeling changes.

Biological significance and challenges: moderate supercoiling influences promoter accessibility and replication dynamics; excessive supercoiling can impede polymerases, promote breaks, or trigger DNA damage responses; cells maintain homeostasis by adjusting torsional state through transcription, replication, and topoisomerase activity.

Research and terminology: Because 'superkoiling' is not a standard term, usage varies; researchers may refer to extreme torsional states in plasmids, genomes, or model systems, often using measurements of linking number, twist, and writhe, or assays that detect supercoiling levels.