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J. Bacteriol. doi:10.1128/JB.00055-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A-Factor and Phosphate-Depletion Signals Are Transmitted to the Grixazone Biosynthesis Genes via the Pathway-Specific Transcriptional Activator GriR

Department of Biotechnology, Graduate School of Agriculture and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan

^* To whom correspondence should be addressed. Email: asuhori{at}mail.ecc.u-tokyo.ac.jp.

	Abstract

Grixazone (GX), which is a diffusible yellow pigment containing a phenoxazinone chromophore, is one of the secondary metabolites under the control of A-factor (2-isocapryloyl-3R-hydroxymethyl--butyrolactone) in Streptomyces griseus. GX production is also induced by phosphate starvation. The whole biosynthesis gene cluster for GX was cloned and characterized. The gene cluster consisting of 13 genes contained six transcriptional units, griT, griSR, griR, griAB, griCDEFG, and griJIH. During cultivation in a phosphate-depleted medium, the six promoters were activated in the order of (i) griR, (ii) griC and griJ, and (iii) griT, griS, and griA. Disruption of griR encoding a SARP-family transcriptional regulator abolished the transcriptional activation of all other genes in the cluster. In addition, ectopic expression of griR from a constitutively active promoter resulted in GX overproduction even in the absence of AdpA, a key transcriptional activator in the A-factor regulatory cascade, and in the presence of phosphate at a high concentration. GriR monomers bound direct repeat sequences in the griC and griJ promoters in a cooperative manner. Therefore, the early active genes (griCDEFG and griJIH), all of which, except for griG encoding a transporter-like protein, encode the GX biosynthesis enzymes, were directly activated by GriR. The transcription of griR was greatly reduced in the presence of phosphate at a high concentration and was hardly detected in the absence of AdpA. These findings showed that both A-factor and phosphate-depletion signals were required for the griR transcription and both signals were transmitted to the GX biosynthesis genes solely via the griR promoter.

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