Ribonuclease A is a pancreatic endoribunuclease that specifically cleaves single-stranded RNA at the 3’ end of pyrimidine residues. Lyophilized powder purified from bovine pancreas.
Exonuclease I (Exo I) is an exonuclease that hydrolyzes single-stranded DNA, one nucleotide at a time from the end, in the 3´→5´ direction. It releases 5´- mononucleotides one after another and leaves the terminal 5´-dinucleotide intact. This 55kDa enzyme, product of the E.coli sbcB gene, does not cleave DNA strands without terminal 3´-hydroxyl groups, as these are blocked by phosphoryl or acetyl groups1. It does not degrade double-stranded DNA. For activity, Exo I requires magnesium (optimal [Mg2+] is 10mM). Exo I is tolerant to a wide variety of buffer conditions (salt, pH, etc), and thus can be added directly to most molecular biology buffers containing magnesium (>1mM), including PCR reaction mixtures.