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A Conserved Inverted Repeat, the LipR Box, Mediates Transcriptional Activation of the Streptomyces exfoliatus Lipase Gene by LipR, a Member of the STAND Class of P-Loop Nucleoside Triphosphatases

Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, D.F., México

Received 21 June 2006/ Accepted 28 July 2006

Expression of the Streptomyces exfoliatus lipA gene, which encodes an extracellular lipase, depends on LipR, a transcriptional activator that belongs to the STAND class of P-loop nucleoside triphosphatases. LipR is closely related to activators present in some antibiotic biosynthesis clusters of actinomycetes, forming the LipR/TchG family of regulators. In this work we showed that purified LipR protein is essential for activation of lipA transcription in vitro and that this transcription depends on the presence of a conserved inverted repeat, the LipR box, located upstream of the lipA promoter. Mutagenesis of the lipA promoter region indicated that most transcription depends on LipR binding to the proximal half-site of the LipR box in close proximity to the –35 region of the promoter. Our experiments also indicated that LipR establishes contact with the RNA polymerase on both sides of the LipR box, since some activation was observed when only the distal half-site was present or when the entire LipR box was moved further upstream. We also showed that the LipR proteins of S. exfoliatus and Streptomyces coelicolor are functionally interchangeable both in vitro and in vivo, revealing the functional conservation of the regulatory elements in these two species.