New regulatory gene that contributes to control of Bacteroides thetaiotaomicron starch utilization genes
New regulatory gene that contributes to control of Bacteroides thetaiotaomicron starch utilization genes
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DOI：
10.1128/jb.183.24.7198-7205.2001
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发表时间：
2001-12-01
影响因子：
3.2
通讯作者：
Salyers, AA
中科院分区：
文献类型：
--
作者：
Cho, KH;Cho, D;Salyers, AA
多形拟杆菌利用淀粉作为碳源和能量。淀粉利用途径的早期步骤，如淀粉结合和淀粉水解，是由sus基因编码的，这些基因的特征已经在以前得到了描述。只有当细胞生长在含有麦芽糖或更高的葡萄糖低聚物的培养基中时，sus结构基因才会表达。sus结构基因的调节由SusR介导，SusR是一种由位于sax结构基因旁边的基因编码的激活剂。具有susR破坏的菌株不能在淀粉上生长，但仍然可以在麦芽糖和麦芽三糖上生长。对不能在麦芽糖和麦芽三糖上生长的转座子产生的突变体的搜索意外地定位了一个称为malR的基因，其调节不受SusR控制的α-葡糖苷酶的表达。虽然susR的中断不影响malR控制基因的表达，但malR的中断降低了sus结构基因的表达。因此，MalR似乎与SusR一起参与调节sus基因。转录融合实验和逆转录PCR实验的结果表明，malR的组成型表达。此外，在质粒上提供的malR的多个拷贝（每个细胞5至10个拷贝）使细胞提取物中的α-葡糖苷酶活性的量增加一倍以上。研究结果表明，B的淀粉利用系统是一个完整的系统。多形核在至少两个水平上由调节蛋白SusR和MalR控制。
Bacteroides thetaiotaomicron uses starch as a source of carbon and energy. Early steps in the pathway of starch utilization, such as starch binding and starch hydrolysis, are encoded by sus genes, which have been characterized previously. The sus structural genes are expressed only if cells are grown in medium containing maltose or higher oligomers of glucose. Regulation of the sus structural genes is mediated by SusR, an activator that is encoded by a gene located next to the sax structural genes. A strain with a disruption in susR cannot grow on starch but can still grow on maltose and maltotriose. A search for transposon-generated mutants that could not grow on maltose and maltotriose unexpectedly located a gene, designated malR, which regulates expression of an alpha -glucosidase not controlled by SusR. Although a disruption in susR did not affect expression of the malR controlled gene, a disruption in malR reduced expression of the sus structural genes. Thus, MalR appears to participate with SusR in regulation of the sus genes. Results of transcriptional fusion assays and reverse transcription-PCR experiments showed that malR is expressed constitutively. Moreover, multiple copies of malR provided on a plasmid (5 to 10 copies per cell) more than doubled the amount of a-glucosidase activity in cell extracts. Our results demonstrate that the starch utilization system of B. thetaiotaomicron is controlled on at least two levels by the regulatory proteins SusR and MalR.