Distinct Activities of Exonuclease 1 and Flap Endonuclease 1 at Telomeric G4 DNA
Figure 3
hFEN1, but not hEXO1, cleaves 5′ nontelomeric G4 DNA flaps and 5′ flaps adjacent to 3′ nontelomeric G4 DNA tails.
(A) Diagram of substrates bearing 5′ or 3′ nontelomeric G4 DNA tails. Lengths of oligonucleotides, flaps, duplex regions and 3′ tails are indicated; asterisk denotes 5′ end-label. (B) Products of digestion of substrates shown in Panel A by hEXO1 (0, 1.2, 2.4 and 3.6 nM) and hFEN1 (4.5, 9.0 and 18.0 nM). Arrows indicate 60 nt undigested 5′-labeled DNA substrates, products of flap endonuclease digestion, and 1 nt product of exonuclease digestion. (C) Quantitation of flap cleavage activity of hEXO1 (0, 0.6, 1.2 and 2.4 nM; diamonds) and hFEN1 (0, 4.5, and 9.0 nM; squares) on substrates shown in Panel A.