THE DISTAL GATA SEQUENCES OF THE SID1 PROMOTER OF USTILAGO-MAYDIS MEDIATE IRON REPRESSION OF SIDEROPHORE PRODUCTION AND INTERACT DIRECTLY WITH URBS1, A GATA FAMILY TRANSCRIPTION FACTOR

The sid1 and urbs1 genes encode L-ornithine N-5-oxygenase and a GATA f amily transcription regulator respectively, for siderophore biosynthes is in Ustilago maydis. The basic promoter and iron-regulatory sequence s of the U.maydis sid1 gene were defined by fusing restriction and Bal 31 nuclease-generated deletion fragments of the promoter region with t he Escherichia coil beta-glucuronidase (GUS) reporter gene, Sequences required for basal expression of sid1 mapped within 1043 bp upstream o f the translation start site and include the first untranslated exon a nd first intron, Sequences needed for iron-regulated expression of sid 1 were localized to a 306 bp region mapping 2.3 and 2.6 kb upstream of the ATG. The 306 bp region contains two G/TGATAA sequences, consensus DNA binding sites of GATA family transcription factors, Deletion or s ite-directed mutation of either or both GATA sequences resulted in der egulated expression of sid1. In vitro DNA binding studies showed that Urbs1 binds to the 3'-GATA site in the 306 bp iron-responsive region, However, deletion of 1.1 kb between the distal GATA sites and the basa l promoter region led to deregulated expression of GUS, indicating tha t these GATA sequences are by themselves insufficient to regulate sid1 . PIE vitro DNA binding and in vivo reporter gene analysis revealed th at siderophores are not corepressors of Urbs1.