Regulation of the yellow pigment biosynthetic genes by a microbial hormone and phosphate depletion

A因子（2-isocapryloyl-3R-hydroxymethyl-γ-butyrolactone）是一种微生物激素，在灰色链霉菌中诱导形态发育和次生代谢。在A因子控制下的次级代谢产物之一是grixazone（GX），它是一种含有吩恶嗪酮发色团的可扩散黄色色素。GX生产也是由磷酸盐消耗诱导的。GX合成基因簇由13个基因组成，有6个转录单位：griT、griSR、griR、griAB、griCDEFG和griJIH。破坏griR，它编码的SARP家族转录调节因子，废除了其他基因的转录簇。重组GriR在体外与格里克和griJ启动子结合。转录的griR没有激活的情况下，A-因子或在存在高浓度的磷酸盐。当griR从组成型活性启动子异位转录时，GX在没有A因子和磷酸盐耗尽信号的情况下过度产生。这些结果表明A因子和磷酸盐耗尽信号都通过GriR传递到GX生物合成基因。另一方面，griZ作为S. griseus M31，GX生产缺陷突变株。griZ在染色体上远离GX生物合成基因簇存在，编码TetR家族转录调节因子。griZ破坏的菌株未能激活griR并产生GX。当griR从griZ破坏菌株中的组成型活性启动子转录时，GX生产恢复。这些结果表明，griZ是必不可少的GX生产和参与激活griR转录。

A-factor (2-isocapryloyl-3R-hydroxymethyl-γ-butyrolactone) serves as a microbial hormone that induces morphological development and secondary metabolism in Streptomyces griseus. One of the secondary metabolites under the control of A-factor is grixazone (GX) which is a diffusible yellow pigment containing a phenoxazinone chromophore. GX production is also induced by phosphate depletion. Because of the regulation of the GX production by both A-factor and phosphate, the biosynthetic gene cluster for GX is a useful material for elucidating the molecular mechanisms by which γ-butyrolactone and phosphate control secondary metabolite formation.The biosynthetic gene cluster for GX consists of 13 genes and there are six transcriptional units : griT, griSR, griR, griAB, griCDEFG, and griJIH. Disruption of griR, which encodes a SARP-family transcriptional regulator, abolished the transcription of other genes in the cluster. Recombinant GriR bound to the griC and griJ promoters in vitro. Transcription of griR was not activated in the absence of A-factor or in the presence of a high concentration of phosphate. When griR was transcribed ectopically from a constitutively active promoter, GX was overproduced without A-factor and phosphate-depletion signals. These results indicated that both A-factor and phosphate-depletion signals are transmitted to the GX biosynthesis genes via GriR.On the other hand, griZ was cloned as a mutated gene in S. griseus M31, a mutant strain deficient in the GX production. griZ exists far away from the GX biosynthetic gene cluster on the chromosome and encodes a TetR-family transcriptional regulator. The griZ-disrupted strain failed to activate griR and to produce GX. When griR was transcribed from a constitutively active promoter in the griZ-disrupted strain, GX production was restored. These results indicated that griZ is essential for the GX production and involved in the activation of griR transcription.