FUNCTIONAL DOMAINS OF THE ARAC PROTEIN

The AraC protein, which regulates the L-arabinose operons in Escherich ia coli, was dissected into two domains that function in chimeric prot eins. One provides a dimerization capability and binds the ligand arab inose, and the other provides a site-specific DNA-binding capability a nd activates transcription. In vivo and in vitro experiments showed th at a fusion protein consisting of the N-terminal half of the AraC prot ein and the DNA-binding domain of the LexA repressor dimerizes, binds well to a LexA operator, and represses expression of a LexA operator-b eta-galactosidase fusion gene in an arabinose-responsive manner. In vi vo and in vitro experiments also showed that a fusion protein consisti ng of the C-terminal half of the AraC protein and the leucine zipper d imerization domain from the C/EBP transcriptional activator binds to a raI and activates transcription from a p(BAD) promoter-beta-galactosid ase fusion gene. Dimerization was necessary for occupancy and activati on of the wild-type AraC binding site.