ribonucleases

Ribonucleases, or RNases, are enzymes that catalyze the hydrolysis of RNA phosphodiester bonds, producing shorter RNA fragments and nucleotides. They function as endoribonucleases, which cleave RNA internally, and exoribonucleases, which remove nucleotides from RNA ends. RNases are found in virtually all living organisms and are central to RNA processing, turnover, quality control, and defense against RNA elements such as viruses in some contexts.

Classification and examples: Major families include the RNase A family of secreted ribonucleases that cleave on the 3′ side of pyrimidines, RNase H enzymes that degrade RNA in RNA–DNA hybrids, and the RNase T2 family, acidic and nonspecific ribonucleases found in plants, animals, and fungi. Exoribonucleases such as the RNB family (e.g., RNase II and RNase R) operate 3′–5′, while the XRN family catalyzes 5′–3′ degradation. In eukaryotes, ribonucleoprotein enzymes such as RNase P and RNase MRP participate in tRNA maturation and rRNA processing, respectively.

Mechanism and properties: Many RNases require divalent metal ions or employ specific catalytic residues within defined active sites. Some enzymes generate 2′,3′-cyclic phosphate intermediates, while others yield 3′-phosphate or 5′-hydroxyl ends, depending on the enzyme and substrate. Substrate range and regulatory features vary across families and organisms.

Biological significance: RNases regulate RNA lifecycles, including mRNA decay, rRNA and tRNA maturation, and quality control of transcripts. They can participate in gene expression regulation, RNA surveillance pathways, and, in some systems, defense against foreign RNAs.

Laboratory notes: RNases are pervasive and robust, making contamination a frequent concern in molecular biology. Work with RNases requires RNase-free reagents and equipment, proper storage, and the use of RNase inhibitors and validated cleanup protocols to prevent unwanted RNA degradation.