ZDNA

Z-DNA is a left-handed form of DNA distinguished by a zigzag sugar-phosphate backbone and a distinct helical geometry that sets it apart from the more common right-handed B-DNA. It tends to form in sequences with alternating purine and pyrimidine bases, most notably stretches of CG repeats, and under conditions that promote torsional stress or high ionic strength. The transition from B-DNA to Z-DNA is dynamic and depends on the local sequence and the cellular environment.

Formation and stability of Z-DNA are influenced by factors such as negative supercoiling, high salt concentrations, and certain chemical modifications of bases. While Z-DNA is relatively unstable under standard physiological conditions, it can be stabilized in specific contexts, especially in regions experiencing transcription-induced torsional stress or in the presence of particular ions and cofactors. In cells, Z-DNA is often considered to be transient and localized to specific genomic regions.

Biological significance of Z-DNA includes its interactions with specialized proteins capable of recognizing the left-handed conformation. Z-DNA binding proteins and domains have been identified, suggesting roles in transcriptional regulation, chromatin organization, and genome stability. However, the extent and mechanisms of Z-DNA’s functional importance in vivo remain active areas of investigation, with ongoing studies addressing how often and where Z-DNA forms under normal cellular conditions.

Detection and study of Z-DNA rely on techniques such as X-ray diffraction, nuclear magnetic resonance, circular dichroism, chemical probing, and the use of Z-DNA–binding proteins as markers. Z-DNA remains a valuable model for understanding DNA conformational flexibility and its potential regulatory implications.