Nucleic Acids Research, 2007, Vol. 35, No. 14 4615 Figure 6. (A) DNA nicking or ds cleavage activity of BsrDI A/B mutants. B cat = catalytic-deﬁcient B subunit. Plasmid pUC19 (2 BsrDI sites) was used as the substrate for nicking or restriction assay. NC, nicked-circular DNA; SC, supercoiled DNA. (B) Run-oﬀ sequencing of gel-puriﬁed, nicked-circular DNA. The expected nicking speciﬁcity of Nt.BsrDI is GCAATGNN# (BsrDI site and the adjacent sequence are shown at the bottom of the ﬁgure). The extra A peak at the end of run-oﬀ sequence was added by the template independent terminal transferase activity of the Taq DNA pol.