Figure 6.

Feedback in PHO84 expression. (A) Expression levels of PHO84 in the BY, RM and the PHO84-RM AS strains. The expression of PHO84 in the AS and RM strains is similar and significantly lower than in BY. The fold difference is calculated relative to the BY strain. Since the AS strain only differs from the BY strain in the PHO84 coding sequence, feedback regulation must act through the PHO84 gene itself. The error bars represent the s.d. of three replicates. All RT–PCR experiments were conducted independently at least three times. (B) A negative feedback loop regulates expression of Pho84 in response to the concentration of intracellular phosphate. When phosphate levels are low, Pho84 is expressed and transports inorganic phosphate into the cell; Pho84 is repressed as intracellular phosphate levels rise. (C) Expression of PHO84 in SC+high-phosphate media compared with that in SC+low-phosphate media for each strain. The cells were harvested 90 min after the addition of phosphate. The AS and RM strains are repressed to a greater extent than BY in response to the addition of phosphate. (D) Weak eQTL that influence the expression of PHO84. These loci are enriched in genes involved in phosphate metabolism and phosphate transport. PHO84 expression links to regions that contain GTR1, NPP1, PHO84, PHO85, PHO86 and PHO87. The width of arrows corresponds to the significance of linkage (P-value for each linkage <0.01; see section Materials and methods).