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Journal of Bacteriology, August 2009, p. 4786-4797, Vol. 191, No. 15
0021-9193/09/$08.00+0     doi:10.1128/JB.00437-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of {gamma}-Butyrolactone Autoregulatory Signaling Gene Homologs in the Angucyclinone Polyketide WS5995B Producer Streptomyces acidiscabies{triangledown}

Frank G. Healy,1* Kevin P. Eaton,1 Prajit Limsirichai,1 Joel F. Aldrich,1 Alaina K. Plowman,1 and Russell R. King2

Department of Biology, Trinity University, San Antonio, Texas 78212,1 Agriculture and Agri-Food Canada, Research Branch, Fredericton Research Centre, Fredericton, New Brunswick, Canada E3B4Z72

Received 31 March 2009/ Accepted 18 May 2009

Organisms belonging to the genus Streptomyces produce numerous important secondary metabolites and undergo a sophisticated morphological differentiation program. In many instances these processes are under the control of {gamma}-butyrolactone (GBL) autoregulatory systems. Streptomyces acidiscabies strain 84.104 produces the secondary metabolite aromatic angucyclinone polyketide WS5995B. In order to explore the role of GBL regulatory circuitry in WS5995B production and morphogenesis in S. acidiscabies, a gene cluster encoding GBL autoregulatory signaling homologs was identified and characterized. Two GBL receptor homologs, sabR and sabS, were found flanking a GBL synthase homolog sabA. Strains carrying mutations in sabS produced elevated levels of WS5995B and displayed conditional morphological defects reminiscent of defects seen in Streptomyces bldA mutants. Notably, sabS possesses a TTA codon predicted to be recognized by tRNAleu. sabA mutants produced higher levels of WS5995B than the wild-type strain but to a lesser extent than the levels of WS5995B seen in sabS mutants. Purified recombinant SabR and SabS were tested for their abilities to bind predicted AT-rich autoregulatory element (ARE) boxes within the sabRAS region. SabS did not bind any DNA sequences in this region, while SabR bound an ARE box in the region upstream of sabS. Quantitative reverse transcription-PCR analysis revealed higher levels of sabS transcript in sabR mutants than in the wild-type strain, suggesting that sabS expression is repressed by SabR. Based on these data, we propose that the S. acidiscabies sabRAS genes encode components of a signaling pathway which participates in the regulation of WS5995B production and morphogenesis.

* Corresponding author. Mailing address: Department of Biology, One Trinity Place, Trinity University, San Antonio, TX 78212. Phone: (210) 999-7242. Fax: (210) 999-7229. E-mail: frank.healy{at}trinity.edu

{triangledown} Published ahead of print on 22 May 2009.

Journal of Bacteriology, August 2009, p. 4786-4797, Vol. 191, No. 15
0021-9193/09/$08.00+0     doi:10.1128/JB.00437-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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