The pleiotropic regulator AdpA-L directly controls the pathway-specific activator of nikkomycin biosynthesis in Streptomyces ansochromogenes

The nikkomycin-producing strain Streptomyces ansochromogenes has a homologue (adpA-L) of the key pleiotropic Streptomyces regulatory gene adpA. Gene disruption and genetic complementation revealed that adpA-L was required for both nikkomycin biosynthesis and morphological differentiation. Transcriptional analysis suggested that the transcription of sanG, the specific activator gene for nikkomycin biosynthesis, was dependent on AdpA-L. In gel-shift and DNase 1 footprinting assays, the purified His6-tagged recombinant AdpA-L protein bound the upstream region of sanG at five sites, which are spread over more than one kilobase of DNA and most of which is inside the transcribed region. A consensus AdpA-L-binding sequence, 5'-TGGCNNVWHN-3' (V: C, A or G; W: A or T; H: A, T or C; N: any nucleotide) was found in these binding sites. Transcriptional analysis of sanG carrying mutated AdpA-L binding sites showed that transcription of sanG was eliminated when site I was mutated and its trascription was decreased when site V was mutated, whereas it was increased when the binding sites II, III or IV were mutated. Meanwhile, nikkomycin production of the mutated site III strain was enhanced comparing with the wild-type strain as control. This work highlights a new level of complexity in the regulation of nikkomycin biosynthesis.