Gilson L, Kuo A, Dunlap P V
Biology Department, Woods Hole Oceanographic Institution, Massachusetts 02543, USA.
J Bacteriol. 1995 Dec;177(23):6946-51. doi: 10.1128/jb.177.23.6946-6951.1995.
In Vibrio fischeri, the autoinducer N-3-oxohexanoyl-L-homoserine lactone (AI-1) governs the cell density-dependent induction of the luminescence operon via the LuxR transcriptional activator. The synthesis of AI-1 from bacterial metabolic intermediates is dependent on luxI. Recently, we found a second V. fischeri autoinducer molecule, N-octanoyl-L-homoserine lactone (AI-2), that in E. coli also activates the luminescence operon via LuxR. A locus independent of luxI was identified as being required for AI-2 synthesis. This 2.7-kb ain (autoinducer) locus was characterized by transposon insertion mutagenesis, deletion and complementation analysis, and DNA sequencing. A single 1,185-bp gene, ainS, was found to be the sole exogenous gene necessary for the synthesis of AI-2 in Escherichia coli. In addition, a V. fischeri ainS mutant produced AI-1 but not AI-2, confirming that in its native species ainS is specific for the synthesis of AI-2. ainS is predicted to encode a 45,580-Da protein which exhibits no similarity to LuxI or to any of the LuxI homologs responsible for the synthesis of N-acyl-L-homoserine lactones in a variety of other bacteria. The existence of two different and unrelated autoinducer synthesis genes suggests the occurrence of convergent evolution in the synthesis of homoserine lactone signaling molecules. The C-terminal half of AinS shows homology to a putative protein in Vibrio harveyi, LuxM, which is required for the synthesis of a V. harveyi bioluminescence autoinducer. Together, AinS and LuxM define a new family of autoinducer synthesis proteins. Furthermore, the predicted product of another gene, ainR, encoded immediately downstream of ainS, shows homology to LuxN, which is similarly encoded downstream of luxM in V. harveyi and proposed to have sensor/regulator functions in the bioluminescence response to the V. harveyi auto inducer. This similarity presents the possibility that AI-2, besides interacting with LuxR, also interacts with AinR under presently unknown conditions.
在费氏弧菌中，自诱导物N-3-氧代己酰基-L-高丝氨酸内酯（AI-1）通过LuxR转录激活因子调控发光操纵子的细胞密度依赖性诱导。由细菌代谢中间体合成AI-1依赖于luxI。最近，我们发现了费氏弧菌的第二种自诱导物分子，N-辛酰基-L-高丝氨酸内酯（AI-2），在大肠杆菌中它也通过LuxR激活发光操纵子。一个独立于luxI的基因座被确定为AI-2合成所必需。通过转座子插入诱变、缺失和互补分析以及DNA测序对这个2.7kb的ain（自诱导物）基因座进行了表征。发现一个单一的1185bp基因ainS是大肠杆菌中合成AI-2所必需的唯一外源基因。此外，费氏弧菌ainS突变体产生AI-1但不产生AI-2，证实了在其天然菌株中ainS对AI-2的合成具有特异性。预测ainS编码一种45580Da的蛋白质，该蛋白质与LuxI或负责多种其他细菌中N-酰基-L-高丝氨酸内酯合成的任何LuxI同源物均无相似性。两个不同且不相关的自诱导物合成基因的存在表明在高丝氨酸内酯信号分子的合成中发生了趋同进化。AinS的C端一半与哈氏弧菌中的一种假定蛋白质LuxM具有同源性，LuxM是哈氏弧菌生物发光自诱导物合成所必需的。AinS和LuxM共同定义了一个新的自诱导物合成蛋白家族。此外，ainS下游紧邻编码的另一个基因ainR的预测产物与LuxN具有同源性，LuxN在哈氏弧菌中同样编码在luxM下游，并被认为在对哈氏弧菌自诱导物的生物发光反应中具有传感器/调节功能。这种相似性表明，除了与LuxR相互作用外，AI-2在目前未知的条件下也可能与AinR相互作用。
