exonucleolisis

Exonucleolysis, also spelled exonucleolisis in some sources, is the enzymatic removal of nucleotides from the ends of DNA or RNA molecules by exonucleases. It is distinguished from endonucleolysis, which cleaves internal phosphodiester bonds within a nucleic acid strand. Exonucleases can act in different directions: 3' to 5' exonucleases remove nucleotides from the 3' end toward the 5' end, while 5' to 3' exonucleases remove from the 5' end toward the 3' end. Some enzymes act on single-stranded substrates, others on double-stranded substrates, and their activity may be processive (removing many nucleotides in one binding event) or distributive (releasing after removing only a few nucleotides).

Biological roles include DNA replication, repair, and RNA metabolism. In DNA replication, exonucleolytic activities participate in proofreading by removing mispaired nucleotides from the growing strand, and in primer removal during lagging-strand synthesis. In DNA repair, exonucleases excise damaged or mismatched nucleotides in various pathways, including mismatch repair and base excision repair. In RNA metabolism, exoribonucleases degrade RNA from the ends, contributing to turnover and quality control of transcripts.

Biological significance and research use: Proper exonucleolysis helps maintain genome stability and normal gene expression. Defects or altered activity can lead to accumulation of DNA damage and are linked to aging, cancer, and other diseases. Exonucleases are studied as potential targets for therapies and as tools in molecular biology.