Rebollo A, Gil J A, Liras P, Asturias J A, Martín J F
Departamento de Ecología, Genética y Microbiología, Facultad de Biología, Universidad de León, Spain.
Gene. 1989 Jun 30;79(1):47-58. doi: 10.1016/0378-1119(89)90091-7.
Phosphate strongly repressed the formation of p-aminobenzoic acid (PABA) synthase, an enzyme involved in candicidin biosynthesis. Expression in Streptomyces lividans of the pabS gene (encoding PABA synthase) of Streptomyces griseus is repressed by phosphate at concentrations above 0.1 mM. However, expression of the pabS gene in Escherichia coli is not regulated by phosphate. Phosphate control of the expression of the pabS gene was observed in all plasmids containing the original 4.5-kb BamHI fragment, whereas no phosphate regulation was found when an upstream 1-kb fragment that carries the pabS promoter was deleted. Using the promoter-probe plasmid pIJ424, a '114-bp' promoter was cloned. Expression of the promoterless kanamycin phosphotransferase gene when fused to the '114-bp' promoter was strongly reduced by phosphate (90% at 5 mM concentration). The '114-bp' promoter has been sequenced and the first transcribed nucleotide identified by S1 mapping. The '114-bp' fragment is A + T-rich (54%), as compared to the Streptomyces genome (70-73% GC). The presence of a phosphate control sequence (pcs) in the upstream region of the pabS gene is proposed.
磷酸盐强烈抑制对氨基苯甲酸（PABA）合酶的形成，该酶参与杀假丝菌素的生物合成。在0.1 mM以上浓度的磷酸盐存在下，灰色链霉菌的pabS基因（编码PABA合酶）在淡紫链霉菌中的表达受到抑制。然而，pabS基因在大肠杆菌中的表达不受磷酸盐调控。在所有含有原始4.5 kb BamHI片段的质粒中均观察到磷酸盐对pabS基因表达的控制，而当缺失携带pabS启动子的上游1 kb片段时，则未发现磷酸盐调控。使用启动子探针质粒pIJ424，克隆了一个“114 bp”的启动子。当无启动子的卡那霉素磷酸转移酶基因与“114 bp”启动子融合时，其表达受到磷酸盐的强烈抑制（在5 mM浓度下抑制90%）。已对“114 bp”启动子进行了测序，并通过S1作图确定了第一个转录核苷酸。与链霉菌基因组（GC含量为70 - 73%）相比，“114 bp”片段富含A + T（54%）。有人提出在pabS基因上游区域存在一个磷酸盐控制序列（pcs）。
