Figure 4.

Single base pair substitutions. The reactions in SfiI assay buffer at 30°C contained 0.5 nM SfiI endonuclease and one of the following duplexes (5′-end-labelled with ³²P in the top strand) at 0.2 µM: AACAA, data points marked by inverted triangles; AAAAC, marked by squares; AAACA, marked by circles. At timed intervals after adding the SfiI, samples were withdrawn from the reactions and analysed as in the Materials and Methods to determine the percent cleavage. The error bars are the standard deviations of the means from three or more separate experiments.