THE ASPERGILLUS-NIDULANS TRANSCRIPTION FACTOR ALCR FORMS A STABLE COMPLEX WITH ITS HALF-SITE DNA - A NMR-STUDY

The Aspergillus nidulans transcription factor AlcR is shown by NMR and gel retardation assay to form a stable complex with oligonucleotide s equences comprising the consensus half-site 5'-TGCGG-3', Apparent mu M dissociation constants are evaluated by both methods, The measured li fetime of the complex is 74 +/- 7 ms at 20 degrees C with the followin g DNA sequence: 5'-C1G2T3G4C5G6G7A8T9C10-3'. The major chemical shift variations upon binding involve both the two adjacent GC pairs (G6 and G7) and, clearly, the AT pairs at both ends of the consensus sequence (T3 and A8), suggesting additional contacts of the protein with the D NA, This extensive and strong interaction with the half-site is anothe r example of the variability in contacts of the fungal DNA-binding pro teins containing Zn(2)Cys(6) domains with their consensus sites. It is the first demonstration that a binuclear cluster protein can bind to DNA as a monomer with strong affinity. (C) 1997 Federation of European Biochemical Societies.