Higashi Tatsuichiro, Iwasaki Yuko, Ohnishi Yasuo, Horinouchi Sueharu
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
J Bacteriol. 2007 May;189(9):3515-24. doi: 10.1128/JB.00055-07. Epub 2007 Mar 2.
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-gamma-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 (i) griR, (ii) griC and griJ, and (iii) griT, griS, and griA. Disruption of griR, which encodes 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 (which encodes 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 griR transcription and both signals were transmitted to the GX biosynthesis genes solely via the griR promoter.
格氏菌素(GX)是一种含有吩恶嗪酮发色团的可扩散黄色色素,是灰色链霉菌中受A因子(2 - 异辛酰基 - 3R - 羟甲基 - γ - 丁内酯)调控的次生代谢产物之一。磷酸盐饥饿也可诱导GX的产生。已克隆并鉴定了GX的整个生物合成基因簇。该基因簇由13个基因组成,包含6个转录单元,即griT、griSR、griR、griAB、griCDEFG和griJIH。在磷酸盐耗尽的培养基中培养时,这6个启动子按以下顺序被激活:(i)griR,(ii)griC和griJ,以及(iii)griT、griS和griA。编码SARP家族转录调节因子的griR的破坏消除了该簇中所有其他基因的转录激活。此外,即使在缺乏A因子调控级联中的关键转录激活因子AdpA且存在高浓度磷酸盐的情况下,从组成型活性启动子异位表达griR也会导致GX过量产生。GriR单体以协同方式结合griC和griJ启动子中的直接重复序列。因此,早期激活的基因(griCDEFG和griJIH),除了griG(编码一种类似转运蛋白的蛋白质)外,均编码GX生物合成酶,它们直接由GriR激活。在高浓度磷酸盐存在下,griR的转录大大降低,在缺乏AdpA的情况下几乎检测不到。这些发现表明,A因子和磷酸盐耗尽信号对于griR转录都是必需的,并且这两个信号仅通过griR启动子传递到GX生物合成基因。