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Figure 2 | BMC Molecular Biology

Figure 2

From: Functional characterization of an alkaline exonuclease and single strand annealing protein from the SXT genetic element of Vibrio cholerae

Figure 2

Qualitative 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).

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