Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/14/1996
Publication Date: N/A
Technical Abstract: In response to iron starvation Ustilago maydis produces the cyclic peptide siderophores ferrichrome and ferrichrome A. sid1 and sid2, two genes required for ferrichrome siderophore biosynthesis have been cloned. sid1 encodes ornithine-N**5-oxygenase while sid2 encodes a ferrichrome peptide synthetase. Partial DNA sequence analysis of sid2 has revealed the presence of three putative amino acid activating domains consistent with a nonribosomal mechanism for ferrichrome peptide synthesis. sid1 and sid2 are genetically and physically linked. As genes involved in secondary metabolites are often clustered in fungi, we anticipate that other genes required for ferrichrome biosynthesis may be associated with sid1 and sid2. A gene with sequence identity to ADE6 of yeast was located adjacent to sid1. DNA distal to sid2 and extending in the opposite direction has yet to be characterized. Regulation of sid1 has been studied by GUS reporter analysis and in vitro gel mobility shift analysis. As expected, GUS activity was regulated by the availability of iron. Sequences required for iron mediated regulation of sid1 were identified by deletion and site-directed mutagenesis. Two GATA motifs located 1.6 kb upstream of the transcription initiation site were required to mediate repression of sid1. Previous studies have led to the cloning of urbs1, a putative repressor of sid1. Gel mobility shift analysis using these motifs as well as GAT mutant derivatives as DNA probes indicated that Urbs1 binds specifically to the GATA sequences of sid1. Mutation of the C- terminal finger motif but not the N-terminal finger motif of Urbs1 significantly reduced DNA binding activity.