DNAcleavage

DNA cleavage refers to the cutting of DNA strands by nucleases, enzymes that hydrolyze phosphodiester bonds within the DNA backbone. Cleavage can occur on one or both strands, producing single-strand breaks or double-strand breaks, and it may be sequence-specific or nonspecific. Endonucleases cleave within a DNA molecule, while exonucleases remove nucleotides from ends. Cleavage can yield blunt ends or overhanging (sticky) ends, depending on the enzyme and mechanism.

Endonucleases include restriction enzymes that recognize short DNA sequences and cut at or near those sites, generating defined fragment lengths. In genetic engineering, programmable nucleases such as zinc finger nucleases (ZFN), transcription activator-like effector nucleases (TALEN), and CRISPR-associated nucleases (CRISPR-Cas) induce double-strand breaks at targeted genomic locations, enabling targeted modification or disruption of genes. Nicks, or single-strand breaks, can be produced by nicking enzymes, which may influence repair outcomes and genome editing strategies.

In biology, DNA cleavage is a fundamental mechanism in replication, repair, recombination, and gene regulation. Cells deploy nucleases in DNA damage responses to process broken DNA ends for repair pathways such as non-homologous end joining (NHEJ) and homologous recombination (HR). Exonucleases participate in resection and maturation of DNA ends, while dedicated repair systems fix damaged sites to maintain genome integrity. DNA cleavage can also be a consequence of genotoxic stress, leading to cell cycle arrest or apoptosis if damage is extensive.

In laboratory settings, DNA cleavage underpins techniques such as restriction digestion for cloning, DNA fingerprinting, and genome editing. It also plays a role in library preparation for sequencing and in various molecular assays that map or quantify DNA fragments.