Disclosed is a product and process, wherein one adds a N-terminal Histamine-Maltose Binding Protein (“MBP”) tag to endonucleases, including restriction endonucleases like Hind III, and binds the tagged fusion protein to a solid support, preferably beads, once the enzyme has digested oligonucleotides in solution, in order to arrest further digestion. Preferred beads for binding the tagged enzyme are magnetic beads, which can easily be removed from solution by binding to a support and then removing it, or can be accumulated by magnetic attraction in a particular region. More preferred are magnetic beads bound to iminodiacetic acid or nitrilotriacetic acid.