BLDA-DEPENDENT EXPRESSION OF THE STREPTOMYCES-EXFOLIATUS M11 LIPASE GENE (LIPA) IS MEDIATED BY THE PRODUCT OF A CONTIGUOUS GENE, LIPR, ENCODING A PUTATIVE TRANSCRIPTIONAL ACTIVATOR

Extracellular lipase synthesis by Streptomyces lividans 66 carrying th e cloned lipase gene (lipA) from Streptomyces exfoliatus M11 was found to be growth phase dependent, since lipase was secreted into the medi um mainly during the stationary phase; S1 nuclease protection experime nts revealed abundant lipA transcripts in RNA preparations obtained du ring the stationary phase but not in those obtained during exponential growth. Transcription from the lipA promoter was dependent on the pre sence of lipR, a contiguous downstream gene with a very high guanine-p lus-cytosine content (80.2%), The deduced lipR product consists of a p rotein of 934 amino acids that shows similarity to known transcription al activators and has a strong helix-turn-helix motif at its C terminu s; this motif is part of a domain homologous to DNA-binding domains of bacterial regulators of the UhpA/LuxR superfamily. The lipR sequence revealed the presence of a leucine residue, encoded by the rare TTA co don, which caused bldA dependence of lipA transcription in Streptomyce s coelicolor A3(2); replacement of the TTA codon by the alternate CTC leucine codon alleviated bldA dependence but not the apparent growth p hase-dependent regulation of lipA transcription, When lipR expression was induced in a controlled fashion during the exponential growth phas e, by placing it under the inducible tipA promoter, lipase synthesis w as shifted to the exponential growth phase, indicating that the timing of lipR expression, and not its bldA dependence, is the main cause fo r stationary-phase transcription of lipA.