Figure 5.

Effect of an internal abasic site or a nick containing a 5′-abasic residue on the nuclease activity of Exo1. (A) Schematic of the duplex DNA substrates used. F, the tetrahydrofuran residue, is a synthetic abasic site analog (51). (Top) The intact abasic site-containing duplex (41F). (Bottom) The single-strand nick 5′-abasic residue-containing duplex (41IF). The asterisk indicates the location at which these DNAs were ³²P-labeled for the experiments in (B). (B) Hex1-N2 degradation of internal and 5′-F-containing substrates. An aliquot of 1 pmol of substrate was incubated with 0, 0.01 or 0.1 ng wild-type Hex1-N2 protein for 20 min at 37°C and the reactions were analyzed on 20% polyacrylamide–8 M urea denaturing gels (see Materials and Methods). The arrows indicate the sizes of the prominent DNA products (22 and 6 nt) and the location of the abasic residue (F).