Mung bean nuclease I. 7. Terminally directed hydrolysis of native DNA

Publisher Website
Google Scholar
Abstract
Under conditions which favor the duplex structure of DNA, mung bean nuclease catalyzes a limited number of double-strand cleavages (probably less than 50) in the interior of native T7 phage DNA. Under conditions which are not as favorable to a tight helical structure, the large duplex polymers previously produced are completely degraded from their termini with a continuous accumulation of mono-, di- and trinucleotides. The terminally directed activity is an intrinsic property of the enzyme molecule because it is inactivated and reactivated in parallel with the single-strand activity and because the 2 activities coelectrophorese on analytical gels. Kinetic measurements indicate that the apparent Km for the terminally directed hydrolysis of native DNA is relatively high. The pH optimum for the hydrolysis of denatured DNA and the terminally directed hydrolysis of native DNA becomes more acidic with increasing salt concentration. The relative preference for single-stranded structures increases as the pH becomes more basic.