The XRE-DUF397 Protein Pair, Scr1 and Scr2, Acts as a Strong Positive Regulator of Antibiotic Production in Streptomyces

The xenobiotic response element (XRE) transcription factors belong to a regulator family frequently found in that are often followed by small proteins with a DUF397 domain. In fact, the pair XRE-DUF397 has been proposed to comprise toxin-antitoxin (TA) type II systems. In this work, we demonstrate that one of these putative TA-systems, encoded by the genes and of , and denominated Scr1/Scr2 (which stands for . ), does not behave as a toxin-antitoxin system under the conditions used as was originally expected. Instead the pair Scr1/Scr2 acts as a strong positive regulator of endogenous antibiotic production in . The analysis of the 19 strains tested determined that overexpression of the pair Scr1/Scr2 drastically induces the production of antibiotics not only in , but also in , and sp. CA-240608. Our work also shows that Scr1 needs Scr2 to exert positive regulation on antibiotic production.