Figure 4.

Varied ionic strengths with BplI and PsrI. For (a) and (b), the reactions contained, in 200 μl of buffer at 37 °C, BplI endonuclease (10 U) and 5 nM SC DNA (³H-labeled): either pJM1 (which has one BplI site; blue triangles) or pJM2 (with two BplI sites; red circles). The buffer was the same as BplI buffer (Table 2) except that the concentration of KOAc had been changed from 66 mM to either (a) 200 mM or (b) 800 mM. For (c) and (d), reactions at 30 °C contained, in 200 μl of buffer, PsrI (2 U) and ³H-labelled SC plasmid (5 nM): either pJM3 (one PsrI site; blue triangles) or pJM4 (two PsrI sites; red circles). The buffer was either PsrI buffer (c) or the same buffer but with 200 mM KOAc instead of 66 mM (d). Samples taken from the reactions at the times indicated were analysed as described in Materials and Methods to determine the concentration of the SC substrate left at each time point: the concentration is shown as a fraction of the SC DNA present at zero time.