Tomono Ayami, Tsai Yisan, Yamazaki Haruka, 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. 2005 Aug;187(16):5595-604. doi: 10.1128/JB.187.16.5595-5604.2005.
A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) triggers streptomycin production by inducing the transcription of strR, encoding the pathway-specific transcriptional activator, through signal transduction in the A-factor regulatory cascade in Streptomyces griseus. AdpA, one of the key transcriptional activators in the cascade, bound two upstream activation sites, approximately at nucleotide positions -270 and -50 with respect to the transcriptional start point of strR, as determined by gel mobility shift assays and DNase I footprinting. Transcriptional analysis of the strR promoter with mutated AdpA-binding sites showed that both sites were required for full transcriptional activation of strR by AdpA. Potassium permanganate footprinting showed that AdpA assisted RNA polymerase in forming an open complex at an appropriate position for transcriptional initiation of strR. Nine transcriptional units within the streptomycin biosynthesis gene cluster, including the strR-aphD operon, depended on StrR, indicating that StrR is the pathway-specific transcriptional activator for the whole gene cluster. Consistent with this, expression of strR under the control of a constitutively expressed promoter in an adpA null mutant caused the host to produce streptomycin.
A因子（2-异辛酰基-3R-羟甲基-γ-丁内酯）通过在灰色链霉菌A因子调控级联反应中的信号转导，诱导编码途径特异性转录激活因子的strR转录，从而触发链霉素的产生。AdpA是该级联反应中的关键转录激活因子之一，通过凝胶迁移率变动分析和DNase I足迹实验确定，它结合在相对于strR转录起始点大约核苷酸位置-270和-50的两个上游激活位点上。对具有突变的AdpA结合位点的strR启动子进行转录分析表明，这两个位点都是AdpA对strR进行完全转录激活所必需的。高锰酸钾足迹实验表明，AdpA协助RNA聚合酶在strR转录起始的合适位置形成开放复合物。链霉素生物合成基因簇内的九个转录单元，包括strR-aphD操纵子，都依赖于StrR，这表明StrR是整个基因簇的途径特异性转录激活因子。与此一致的是，在adpA缺失突变体中，在组成型表达启动子控制下的strR表达导致宿主产生链霉素。
