CLONING AND CHARACTERIZATION OF THE GENE (FARA) ENCODING THE RECEPTORFOR AN EXTRACELLULAR REGULATORY FACTOR (IM-2) FROM STREPTOMYCES SP STRAIN FRI-5

IM-2 is a butyrolactone autoregulator that controls production of blue pigment and nucleoside antibiotics in Streptomyces sp, strain FRI-5, An IM-2-specific receptor gene, farA, was cloned from strain FRI-5, an d nucleotide sequencing revealed that the farA gene consists of 666 bp encoding a 221-amino-acid protein of 24.3 kDa with an NH2-terminal am ino acid sequence identical to that of purified native receptor. Anoth er gene, farX; encoding a homolog of AfsA of Streptomyces griseus, was present upstream of farA. The monocistronic nature of the farA transc ript was shown by Northern blot hgbridization, and the transcript leve l increased upon addition of IM-21. Recombinant FarA expressed in and purified from E. coli showed clear ligand specificity toward IM-2, wit h a dissociation constant (K-d) for [H-3]IM-2-C-5 of 18.2 nM. FarA sho wed high overall homology to BarA (virginiae butanolide receptor from S. virginiae) and ArpA (A-factor receptor from S. griseus), Sequence a lignment of the three receptor proteins revealed that the NH2-terminal region containing a helix-turn-helix DNA binding motif was highly con served, The DNA binding motif is common in procaryotic repressors of t he TetR family, suggesting that all the Streptomyces autoregulator rec eptors may act as transcriptional repressors.