The LuxR family members GdmRI and GdmRII are positive regulators of geldanamycin biosynthesis in Streptomyces hygroscopicus 17997

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Abstract
The recent sequencing of the DNA region of the geldanamycin post-polyketide synthase (PKS) modification gene clusters revealed the presence of two regulatory genes: gdmRI (2,907 bp) and gdmRII (2,766 bp). The deduced products of gdmRI and gdmRII (968 and 921 amino acid residues, respectively) were identified as homologues of the LuxR transcriptional regulatory proteins. Inactivation by gene replacement of gdmRI or gdmRII in the Streptomyces hygroscopicus 17997 genome resulted in a complete loss of geldanamycin production. Complementation by a plasmid carrying gdmRI or gdmRII restored geldanamycin production, suggesting that the products of these two regulatory genes are positive regulators that are required for geldanamycin biosynthesis. The gdmRI transcript was detected in the ΔgdmRII mutant, and the gdmRII was detected in the ΔgdmRI mutant, indicating that the two genes are transcribed independently and do not regulate each other. Time course of gene expression analysis by RT-PCR of the geldanamycin biosynthetic genes showed that the transcription of gdmRI and gdmRII correlates with that of genes involved in polyketide biosynthesis, but not with the post-PKS modification gene gdmN, whose transcription is initiated earlier. gdmRI or gdmRII gene disruptants did not transcribe the polyketide biosynthetic related genes pks, gdmF, and gdnA-O-P, but did trancribe gdmN. These results demonstrated that gdmRI and gdmRII are pathway-specific positive regulators that control the polyketide biosynthetic genes in geldanamycin biosynthsis, but not the post-PKS modification gene, gdmN.