Rech S, Deppenmeier U, Gunsalus R P
Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90024.
J Bacteriol. 1995 Feb;177(4):1023-9. doi: 10.1128/jb.177.4.1023-1029.1995.
The mod (chlD) locus at 17 min on the Escherichia coli chromosome encodes a high-affinity molybdate uptake system. To further investigate the structure and regulation of these genes, the DNA region upstream of the previously identified modBC (chlJD) genes was cloned and sequenced. A single open reading frame, designated modA, was identified and appears to encode a periplasmic binding protein for the molybdate uptake system. To determine how the mod genes are regulated in response to molybdate, nitrate, and oxygen, we constructed a series of mod-lacZ operon fusions to the upstream region and introduced them in single copy onto the E. coli chromosome. Whereas molybdate limitation resulted in elevated mod-lacZ expression, neither oxygen nor nitrate had any significant effect on gene expression. A regulatory motif, CATAA, located at the modA promoter was identified and shown to be required for molybdate-dependent control of the modABCD operon. Mutations within this sequence resulted in nearly complete derepression of gene expression and suggest that transcription of the operon is mediated by a molybdenum-responsive regulatory protein.
大肠杆菌染色体上17分钟处的mod（chlD）位点编码一种高亲和力的钼酸盐摄取系统。为了进一步研究这些基因的结构和调控，对先前鉴定的modBC（chlJD）基因上游的DNA区域进行了克隆和测序。鉴定出一个单一的开放阅读框，命名为modA，它似乎编码钼酸盐摄取系统的周质结合蛋白。为了确定mod基因如何响应钼酸盐、硝酸盐和氧气进行调控，我们构建了一系列mod-lacZ操纵子融合体到上游区域，并将它们单拷贝导入大肠杆菌染色体。虽然钼酸盐限制导致mod-lacZ表达升高，但氧气和硝酸盐对基因表达均无显著影响。在modA启动子处鉴定出一个调控基序CATAA，它被证明是modABCD操纵子依赖钼酸盐调控所必需的。该序列内的突变导致基因表达几乎完全去阻遏，这表明操纵子的转录由一种钼响应调节蛋白介导。
