Transcriptional downregulation is widely used for metabolic flux control. Here, marO, a cis-element of Escherichia colimar operator, was explored to engineer promoters of Saccharomyces cerevisiae for downregulation. First, the ADH1 promoter (P_ADH1) and its enhanced variant P_UADH1 were engineered by insertion of marO into different sites, which resulted in decrease in both gfp5 transcription and GFP fluorescence intensity to various degrees. Then, marO was applied to engineer the native ERG1 and ERG11 promoters due to their importance for accumulation of value-added intermediates squalene and lanosterol. Elevated squalene content (4.9-fold) or lanosterol content (4.8-fold) and 91 or 28% decrease in ergosterol content resulted from the marO-engineered promoter P_ERG1(M5) or P_ERG11(M3), respectively, indicating the validity of the marO-engineered promoters in metabolic flux control. Furthermore, squalene production of 3.53 g/L from cane molasses, a cheap and bulk substrate, suggested the cost-effective and promising potential for squalene production.

中文翻译：

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在酿酒酵母中设计顺式元素，通过下调下游代谢通量来有效积累增值化合物角鲨烯

转录下调被广泛用于代谢通量控制。在这里，研究了大肠杆菌mar操纵子的顺式元件marO来设计酿酒酵母的启动子以进行下调。首先，ADH1启动子（_PADH1）及其增强变体_{PU UADH1}通过将marO插入不同位点进行工程改造，导致gfp5转录和GFP 荧光强度都有不同程度的降低。然后，marO被应用于设计原生ERG1和ERG11促进剂，因为它们对于增值中间体角鲨烯和羊毛甾醇的积累很重要。marO工程启动子 P _ERG1(M5)或 P _ERG11(M3)分别导致角鲨烯含量（4.9 倍）或羊毛甾醇含量（4.8 倍）升高，麦角甾醇含量降低 91% 或 28% ，表明代谢通量控制中的marO工程启动子。此外，从甘蔗糖蜜中生产 3.53 g/L 的角鲨烯，这是一种廉价的大块底物，表明角鲨烯生产具有成本效益和前景。