Figure 4

WRN exonuclease can digest 3' overhangs of sufficient length. A) Structures of the 3' overhang substrates. Unlabeled G45 oligomer was annealed to labeled C70, C65, C60, C55, or C50 oligomer to create 45 bp substrates with single-stranded 3' overhangs of 5–25 nt as indicated. The positions of radiolabels are depicted by asterisks; "P" represents the phosphate moiety added to the 3' end of the unlabeled G45 strand to prevent WRN degradation. B) Wild type WRN (2.7 nM) was incubated without ATP for the indicated times with the 5, 10, 15, 20, or 25 nt 3' overhang substrate (0.25 nM) or their single-stranded C50, C55, C60, C65, or C70 building blocks (0.25 nM) and assayed for exonuclease activity as described in Methods.