IRON-REGULATED DNA-BINDING BY THE AFT1 PROTEIN CONTROLS THE IRON REGULON IN YEAST

Iron deprivation of Saccharomyces cerevisiae induces transcription of genes required for high-affinity iron uptake. AFT1 mediates this trans criptional control. In this report, the 5'-flanking region of FET3, wh ich encodes a copper-dependent oxidase required for iron transport, wa s analyzed and found to contain a DNA sequence responsible for AFT1-re gulated gene expression. AFT1 was capable of interacting specifically with this DNA sequence. A core element within this DNA sequence necess ary for the binding of AFT1 was also determined. In vivo footprinting demonstrated occupancy of the AFT1 binding site in cells deprived of i ron and not in cells grown in the presence of iron. Thus, the environm ental signal resulting from iron deprivation was transduced through th e regulated binding of AFT1 to the FET3 promoter, followed by the acti vation of transcription. A regulon of genes under the control of AFT1 could be defined. AFT1 was able to bind to a consensus binding site (P yPuCAC-CCPu) in the 5' region of FRE1, FRE2, FTR1, FTH1 and CCC2.