a, Expression of the K. lactis STE2 reporter in the absence of pheromone. Expression is shown as mean for three independent isolates +/− s.d. Three asterisks, P < 0.001; two asterisks, P < 0.01, by ANOVA followed by Tukey’s honest significant difference; for clarity, only the most relevant relationships are shown b, Diagram of the cis-regulatory sites in the L. kluyveri STE2 promoter. c, The STE2 gene promoter from L. kluyveri was fused to GFP and integrated into the L. kluyveri genome. Ste12 and α2 binding sites were introduced by point mutation, and each construct was measured in four independent genetic isolates by flow cytometry. Shown is the mean fluorescence for four independent isolates +/− s.d. Statistical tests shown as in panel a. d, Constructs with added Ste12 binding sites were tested for the ability to compensate for the deletion of the MATa2 gene in K. lactis. Shown as in panel a.