FIG. 5.
The constitutive SPS sensor mutants require less inducer to give strong signaling. Cells growing exponentially in SD medium were exposed to leucine at various concentrations, and Stp1-ZZ processing was monitored. EC50 (apparent Kd) was calculated using SigmaPlot 2000 by fitting the data to y = y0 + ax/(b + x), where b is EC50. In each panel for the mutants, the indicated values for the mean and the standard error of the mean for EC50 are derived from three experiments carried out in identical ways on different days; data points and the fitted curve represent one of the three experiments. The indicated mutations were present as inserts in the centromere-based and URA3-based vector pRS316 in ura3 strains deleted for the corresponding wild-type (wt) SSY5, PTR3, or SSY1 gene, respectively. In the upper panel, the chromosomal SSY5 deletion was complemented by a wild-type SSY5 gene harbored in pRS316 (pSSY5).