FIG. 4.

GΔ228-Uve1p mismatch endonuclease and GΔ228-Uve1p UV photoproduct endonuclease compete for the same substrates. GΔ228-Uve1p was incubated with 3′-end-labeled duplex *CX/AY-31mer (Table 1) in the presence of increasing amounts of unlabeled duplex CPD-30mer (squares), duplex GX/CY-31mer (triangles), or duplex CX/AY-31mer (circles). The Uve1p-mediated DNA cleavage products were analyzed on DNA sequencing gels, and the extent of strand scission was quantified by PhosphorImager analysis (Materials and Methods). Uve1p activity is expressed as percentage of the cleavage observed relative to that observed in the absence of any competitor (defined as 100% activity). The error bars indicate the mean ± standard deviation from three separate experiments.