Figure 1. Iron deficiency alters transcript levels of ergosterol biosynthesis (ERG) genes. 
(B) Kinetics of ERG mRNA levels under iron deficiency in both wild-type FY2609 and BY4741 strains grown for 7 h (FY2609 strain) or 9 h (BY4741 strain) in presence of the iron chelator BPS. The mRNA levels of the indicated ERG genes were determined by RT-qPCR and were normalized with ACT1. Ct values were interpolate using a standard curve generated for each primer pair from serial dilutions of a pool of all samples. Finally, the average and standard deviation (SD) of three biologically independent experiments is calculated and normalized with ACT1.

Figure 2. Deletion of UPC2 and ECM22 limits the up-regulation of ERG genes under iron deficiency. 
WT (W303), upc2delta (referred as “u”), ecm22delta (“e”) and upc2deltaecm22delta (“ue”) cells were grown for 9 h in presence of BPS. The mRNA levels of the indicated ERG genes were determined by RT-qPCR as described in the Figure 1. The statistical analysis of the relative gene expression was performed by the pair wise fixed reallocation randomization test (Pfaffl et al., 2002) using the InfoStat software.

Figure 3. Deletion of HAP1 up-regulates ERG gene expression under iron deficiency. 
WT (BY4741) and hap1delta (referred as “HAP1”) cells were grown for 7 h in medium with or without BPS. The mRNA levels of the indicated ERG genes were determined by RT-qPCR as described in the Figure 1. The existence of statistically significant differences was evaluated with tailed t-student test.

Figure 4. Hap1 is recruited to the promoters of ERG genes under both iron-sufficient and iron-deficient conditions. 
WT (FY2609) cells expressing untagged HAP1 (NO TAG) or HAP1 fused to a myc epitope tag (TAG) were grown as described in Figure 3. Proteins were extracted and immunoprecipitated with anti-myc antibody, and binding to ERG promoter regions was determined by RT-qPCR and analysed as described in Figure 3.

Figure 5. Tup1 is recruited to ERG gene promoters by Hap1 in iron-deficient conditions. WT (BY4741) cells expressing untagged TUP1, and WT and hap1delta cells expressing TUP1 fused to a myc epitope tag, were grown as described in Figure 3. The ChIP experiments were performed as in Figure 4.

Figure 6. Sterols profile of hap1delta cells and regulatory model. (A) Yeast WT (FY2609) and hap1delta cells were grown for 9 h in SC without (+Fe) or with 100 µM BPS (–Fe). Sterol species were quantified by gas chromatography mass spectrometry and their relative abundance was calculated. Finally, the average and SD of four biologically independent experiments is calculated. Statistically significant differences were evaluated with a two-factor factorial design using analysis of variance (ANOVA) and Tukey's text.