Mung-bean nuclease 1 was first purified by Sung and Laskowski (1) in 1962 from mung-bean sprouts (Phaseolus aureus). It belongs to the class of enzymes EC 188.8.131.52., which has a preference for single-stranded nucleic acid substrates, lacks sugar specificity, and hydrolyzes single-stranded substrates to produce products with 5-phoshoryl and 3-hydroxl termini, ranging fro mono-to, at least, heptanucleotides. Although it shows a preference for single-stranded nucleic acids over double-stranded of 30,000-fold (2), used in high concentrations with extended incubation times, mung-bean nuclease 1 will completely degrade double-stranded DNA (3-5). Mung-bean nuclease 1 is also reported to show a separate 3-(1)-monophosphatase activity (6). Mung-bean nuclease 1 is a zinc metalloenzyme that requires Zn2+ and a reducing agent, such as cysteine, for both activity and stability.