Exonuclease I digests ssDNA in a 3´ to 5´ direction, 1-3 but does not digest dsDNA. Although it requires the presence of magnesium and a free 3´-hydroxyl terminus for activity, it is active under a wide variety of buffer conditions and can be added directly into most reaction mixes. Exonuclease I can be heat-inactivated by incubation at 80 °C for 15 minutes.
Applications
- Removal of residual ssDNA, including oligos, from reaction mixes.
- Removal of ssDNA from nucleic acid mixtures.
Figure 1. Specificity of Exonuclease I for ssDNA. 200 ng of EcoR I-linearized pUC19 dsDNA and 1 µg of a 100-mer ssDNA oligo were mixed in 1X TA Buffer and incubated at 37°C for 20 min in the absence or presence of 10 units of Exonuclease I. As seen on this 1% agarose gel, Exonuclease I completely digested the linear ssDNA oligo, but left the linearised plasmid dsDNA intact. Lane 1, size markers; Lane 2, minus Exo I; Lane 3, plus Exo I.
References
- Lehman, I.R. and Nussbaum, A.L. (1964) J. Biol. Chem.
239, 2628.
- Kushner, S.R. et al. (1971) Proc. Natl. Acad. Sci.
USA
68, 824.
- Kushner, S.R. et al. (1972) Proc. Natl. Acad. Sci. USA
69, 1366.