Gostick D O, Griffin H G, Shearman C A, Scott C, Green J, Gasson M J, Guest J R
Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
Mol Microbiol. 1999 Mar;31(5):1523-35. doi: 10.1046/j.1365-2958.1999.01298.x.
Global regulatory circuits of the type mediated by CRP and FNR in Escherichia coli were sought in Lactococcus lactis to provide a basis for redirecting carbon metabolism to specific fermentation products. Using a polymerase chain reaction (PCR) approach, two genes (flpA and flpB) encoding FNR-like proteins (FlpA and FlpB) with the potential for mediating a dithiol-disulphide-dependent regulatory switch, were identified. Transcript analysis indicated that they are distal genes of two paralogous operons, orfX-orfY-flp, in which the orfX and orfY genes were predicted to encode binding domain components of cation ATPases and storage proteins respectively. The corresponding promoters were each associated with a potential FNR site (TTGAT----ATCAA) at positions +4.5 (flpA operon) and -42.5 (flpB operon), suggesting that the respective operons might be negatively and positively autoregulated. The incomplete open reading frames (orfWA/B) located upstream of each operon were predicted to encode additional components of paralogous cation ATPases. No phenotypic effects were detected in flpA and flpB single mutants, but the double mutant had a lower intracellular zinc content, an increased sensitivity to hydrogen peroxide and an altered polypeptide profile (as determined by two-dimensional gel electrophoresis): formate production was not affected. It was concluded tentatively that FlpA and FlpB regulate overlapping modulons, including systems concerned with zinc uptake, in response to metal ion or oxidative stress.
为了找到将碳代谢重定向至特定发酵产物的基础，在乳酸乳球菌中寻找了由大肠杆菌中的CRP和FNR介导的那种全局调控回路。采用聚合酶链反应（PCR）方法，鉴定出了两个编码FNR样蛋白（FlpA和FlpB）的基因（flpA和flpB），它们有可能介导一种依赖二硫醇-二硫化物的调控开关。转录分析表明，它们是两个旁系同源操纵子orfX-orfY-flp的远端基因，其中orfX和orfY基因预计分别编码阳离子ATP酶和储存蛋白的结合域组件。相应的启动子在+4.5（flpA操纵子）和-42.5（flpB操纵子）位置分别与一个潜在的FNR位点（TTGAT----ATCAA）相关联，这表明各自的操纵子可能分别受到负向和正向自调控。预计位于每个操纵子上游的不完整开放阅读框（orfWA/B）编码旁系同源阳离子ATP酶的其他组件。在flpA和flpB单突变体中未检测到表型效应，但双突变体的细胞内锌含量较低，对过氧化氢的敏感性增加，多肽图谱发生改变（通过二维凝胶电泳确定）：甲酸盐产量未受影响。初步得出结论，FlpA和FlpB响应金属离子或氧化应激调节重叠的调节子，包括与锌摄取有关的系统。
