Transcriptional regulation of the aconitase genes (acnA and acnB) of Escherichia coli
Transcriptional regulation of the aconitase genes (acnA and acnB) of Escherichia coli
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DOI：
10.1099/00221287-143-12-3795
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发表时间：
1997-12-01
期刊：
影响因子：
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通讯作者：
Guest, JR
中科院分区：
文献类型：
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作者：
Cunningham, L;Gruer, MJ;Guest, JR
大肠杆菌含有两个差异调节的乌头酸酶基因acnA和acnB。通过引物延伸分析鉴定了两个acnA启动子和一个acnB启动子，所述两个acnA启动子从acnA编码区上游407 bp（P1（acnA））和50 bp（P2（acnA））的起始点转录，所述一个acnB启动子从acnB编码区上游95 bp的起始点转录。通过北方印迹杂交检测到2.8 kb acnA单顺反子转录物，但仅在氧化还原应激（甲基紫精处理）培养物中，并且在指数期但非静止期培养物中检测到2.5 kb acnB单顺反子转录物。这些发现与之前的观察一致，即acnA特异性地受到SoxRS介导的激活，而acnB编码在生长周期中比AcnA更早合成的主要顺乌头酸酶。对acn-lacZ基因融合体和更广泛的转录调控因子的进一步研究表明，acnA表达由sigma（38）从P1（acnA）启动，从P2（acnA）直接或间接地被CRP、FruR、Fur和SoxRS激活，最终被ArcA和FNR抑制。相反，acnB的表达被CRP激活，并被来自P-acnB的ArcA、FruR和Fis抑制。对fum-lacZ融合体的比较研究表明，fumC的转录，而不是fumA或fumB的转录，是由含有sigma的RNA聚合酶启动的（38）。它的结论是，AcnB是主要的柠檬酸循环酶，而AcnA是一个有氧静止相酶，是专门由铁和氧化还原应激诱导。
Escherichia coli contains two differentially regulated aconitase genes, acnA and acnB. Two acnA promoters transcribing from start points located 407 bp (P1(acnA)) and 50 bp (P2(acnA)) upstream of the acnA coding region, and one acnB promoter (P-acnB) with a start point 95 bp upstream of the acnB coding region, were identified by primer extension analysis. A 2.8 kb acnA monocistronic transcript was detected by Northern blot hybridization, but only in redox-stressed (methyl-viologen-treated) cultures, and a 2.5 kb acnB monocistronic transcript was detected in exponential-but not stationary-phase cultures. These findings are consistent with previous observations that acnA is specifically subject to SoxRS-mediated activation, whereas acnB encodes the major aconitase that is synthesized earlier in the growth cycle than AcnA. Further studies with acn-lacZ gene fusions and a wider range of transcription regulators indicated that acnA expression is initiated by sigma(38) from P1(acnA), and from P2(acnA) it is activated directly or indirectly by CRP, FruR, Fur and SoxRS, end repressed by ArcA and FNR. In contrast, acnB expression is activated by CRP and repressed by ArcA, FruR and Fis from P-acnB. Comparable studies with fum-lacZ fusions indicated that transcription of fumC, but not of furnA or fumB, is initiated by RNA polymerase containing sigma(38). It is concluded that AcnB is the major citric acid cycle enzyme, whereas AcnA is an aerobic stationary-phase enzyme that is specifically induced by iron and redox-stress.