Figure 7. XthA displays a metal ion dependent 3′→5′ exonuclease activity on a large variety of substrates.

Schematic diagram of oligonucleotide substrates (refer Table 1 for details) in which asterisk (*) denotes the radioactively labeled γ-³²P terminus. (A) 20 fmol of 5′ end-labeled substrate subSS-Exo was incubated without protein (np,lane 1), with 2 fmol of either End (lane 2) or XthA (lane 3) in a buffer containing 10 mM MgCl₂ for 15 min at 37°C. (B) 20 fmol of 5′ end-labeled substrate subDS-REC (3′ recessed substrate) was incubated without protein (lane 1), with 2 fmol of XthA without any metal (lane 2), XthA in a buffer containing 10 mM MgCl₂ (lane 3) or XthA in a buffer containing 10 mM MnCl₂ (lane 4). (C) 20 fmol of each of the 5′ end-labeled DNA substrates (subDS-REC, subDS-BLUNT and subDS-NICK) were incubated in the absence (–) or presence (+) of 10 fmol of End (lanes 1–6) and XthA (lanes 7–12).