Fig. 6.

Hap1 and Hap4 are involved in the iron-responsive expression of CYC1. (A) Wild-type (BY4742) cells and the hap1Δ and hap2Δ isogenic deletion strains were transformed with reporter plasmid pCYC1-hRluc, pΔUAS1-hRluc, or pΔUAS2-hRluc carrying the indicated CYC1 promoters (Fig. 5A). Cells were cultivated under iron-replete (+Fe) and iron-depleted (−Fe) conditions for 24 h, and the Renilla luciferase-derived luminescence was determined. (B) Expression of the different CYC1 promoter constructs was determined in hap4Δ and wild-type cells overproducing Hap4 (Hap4↑) as described for panel A. (C) The ratio of the iron-responsive expression was calculated from the quotas of the expression of the different CYC1 promoter constructs under iron-replete and iron-deprived conditions for the indicated strains in panels A and B. (D) Wild-type cells expressing the C. elegans heme importer CeHRG4, which harbored the reporter plasmid pCYC1-Luc2, were cultivated under iron-depleting conditions and supplemented with increasing amounts of hemin for 16 h, and the luciferase-derived luminescence was determined. Error bars indicate the SEM (n ≥ 4). ORF, open reading frame.