Figure 2From: Functional characterization of an alkaline exonuclease and single strand annealing protein from the SXT genetic element of Vibrio choleraeQualitative analysis of the metal ion dependence, DNA substrate preferences and mode of digestion of the SXT-Exo alkaline exonuclease. Panel A: Agarose gel showing ability of SXT-Exo to digest linear dsDNA (NdeI-linerized pET28a; lanes 2-5), circularized dsDNA (undigested pET28a; lanes 6 and 7), circularized ssDNA (M13 phage DNA; lanes 8 and 9) in Tris-HCl pH7.4, 50 mM NaCl with/without 10 mM MgCl2; λ-HindIII (NEB) DNA ladder (lane1). Panel B: Agarose gel showing the ability of SXT-Exo and lambda-Exo to digest 5'-phosphorylated linear dsDNA substrates ('unmodified'; lanes 2, 3, 6 and 7), compared with analogous 5'-phosphorylated linear dsDNA substrates containing 3 consecutive phosphorothioate linkages at the 5'-termini of each strand (PT-modified; lanes 4, 5, 8 and 9). The 712 bp 'unmodified' or 'PT-modified' dsDNA substrates (0.1 mg) were incubated at 37°C with lambda-Exo (3 μg) or SXT-Exo (30 μg) in Tris-HCl, (25 mM, pH7.4), 50 mM NaCl, 10 mM MgCl2 (total volume 40 μl). Aliquots (20 μl) were quenched (20 mM EDTA + 1% SDS) immediately, and after 30 mins, and analyzed on 1% agarose TAE gels. 1 Kb Plus DNA Ladder (Invitrogen; lane 1). Panel C: Agarose gel showing time-course of digestion of 5'-phosphorylated linear dsDNA (NdeI-linearized pET28a, 0.56 pmol) by SXT-Exo (50 pmol of trimers) in Tris-HCl pH7.4, 50 mM NaCl, 10 mM MgCl2; at 37°C, with aliquots removed at times indicated (0-160 minutes; lanes 2-11); 1 Kb Plus DNA Ladder (lane 1).Back to article page