Masuda Nobuhisa, Church George M
Department of Genetics, Warren Alpert Building, Room 513, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115, USA.
Mol Microbiol. 2003 May;48(3):699-712. doi: 10.1046/j.1365-2958.2003.03477.x.
Overexpression of the response regulator EvgA confers an acid-resistant phenotype to exponentially growing Escherichia coli. This acid resistance is partially abolished by deletion of ydeP, yhiE or ydeO, genes induced by EvgA overexpression. Microarray analysis identified two classes of operons (genes). The first class contains seven operons induced by EvgA overexpression in the absence of ydeO, an AraC/XylS regulator gene. The second class contains 12 operons induced by YdeO overexpression. Operons in the second class were induced by EvgA overexpression only in the presence of ydeO. EvgA is likely to directly upregulate operons in the first class, and indirectly upregulate operons in the second class via YdeO. Analysis using the motif-finding program alignace identified an 18 bp inverted repeat motif in six upstream regions of all seven operons directly regulated by EvgA. Gel mobility shift assays showed the specific binding of EvgA to the six sequences. Introduction of mutations into the inverted repeats upstream of ydeP and b1500-ydeO resulted in reduction in EvgA-induced ydeP and ydeO expression and acid resistance. These results suggest that EvgA binds to the inverted repeats and upregulates the downstream genes. Overexpression of YdeP, YdeO and YhiE conferred acid resistance to exponentially growing cells, whereas GadX overexpression did not. Microarray analysis also identified several GadX-activated genes. Several genes induced by overexpression of YdeO and GadX overlapped; however, yhiE was induced only by YdeO. The acid resistance induced by YdeO overexpression was abolished by deletion of yhiE, gadC, slp-yhiF, hdeA or hdeD, genes induced by YdeO overexpression, suggesting that several genes orchestrate YdeO-induced acid resistance. We propose a model of the regulatory network of the acid resistance genes.
应答调节因子EvgA的过表达赋予指数生长期的大肠杆菌耐酸表型。这种耐酸性通过缺失ydeP、yhiE或ydeO（由EvgA过表达诱导的基因）而部分消除。微阵列分析鉴定出两类操纵子（基因）。第一类包含在不存在ydeO（一种AraC/XylS调节基因）的情况下由EvgA过表达诱导的七个操纵子。第二类包含由YdeO过表达诱导的12个操纵子。第二类操纵子仅在存在ydeO的情况下由EvgA过表达诱导。EvgA可能直接上调第一类操纵子，并通过YdeO间接上调第二类操纵子。使用基序查找程序alignace进行的分析在所有七个由EvgA直接调控的操纵子的六个上游区域中鉴定出一个18 bp的反向重复基序。凝胶迁移率变动分析表明EvgA与这六个序列特异性结合。在ydeP和b1500-ydeO上游的反向重复序列中引入突变导致EvgA诱导的ydeP和ydeO表达及耐酸性降低。这些结果表明EvgA与反向重复序列结合并上调下游基因。YdeP、YdeO和YhiE的过表达赋予指数生长期细胞耐酸性，而GadX过表达则没有。微阵列分析还鉴定出几个由GadX激活的基因。由YdeO和GadX过表达诱导的几个基因重叠；然而，yhiE仅由YdeO诱导。YdeO过表达诱导的耐酸性通过缺失yhiE、gadC、slp-yhiF、hdeA或hdeD（由YdeO过表达诱导的基因）而消除，这表明几个基因协同调节YdeO诱导的耐酸性。我们提出了一个耐酸性基因调控网络的模型。
