Fig. 4.

BfiI hydrolysis of the PTO-modified and unmodified DNA. (A) Representations of the 14/15 substrates (Table 1) with either R_p–or S_p–PTO linkages at the site of bottom-strand cleavage by BfiI are shown. (B) Extents of DNA cleavage were measured in single-turnover reactions of BfiI (see Materials and Methods) on unmodified DNA (open diamonds) or PTO-substituted DNA (open circles for the R_p and crosses for the S_p derivatives). The solid lines are the best fits to single exponentials to the data, which gave rate constants of 2.0 ± 0.3 s⁻¹ for the unmodified DNA and 0.0034 ± 0.0003 s⁻¹ for the R_p and the S_p substrates.