Ezezika Obidimma C, Collier-Hyams Lauren S, Dale Haley A, Burk Andrew C, Neidle Ellen L
Microbiology Department, 527 Biological Sciences Building, University of Georgia, Athens, GA 30602-2605, USA.
Appl Environ Microbiol. 2006 Mar;72(3):1749-58. doi: 10.1128/AEM.72.3.1749-1758.2006.
Two LysR-type transcriptional regulators, BenM and CatM, control benzoate consumption by the soil bacterium Acinetobacter baylyi ADP1. These homologs play overlapping roles in the expression of multiple genes. This study focuses on the benABCDE operon, which initiates benzoate catabolism. At this locus, BenM and CatM each activate transcription in response to the catabolite cis,cis-muconate. BenM, but not CatM, additionally responds to benzoate as an effector. Regulation by CatM alone is insufficient for growth on benzoate as the sole carbon source. However, three point mutations independently increased CatM-activated benA transcription and enabled growth on benzoate without BenM. Two mutations generate variants with one amino acid change in the 303-residue CatM, CatM(V158M) and CatM(R156H). These substitutions affected regulation of benA differently than that of catB, another CatM-regulated gene involved in benzoate catabolism. In relation to CatM, CatM(V158M) increased cis,cis-muconate-dependent transcription of benA but decreased that of catB. CatM(R156H) increased effector-independent expression of catB compared to CatM. In contrast, cis,cis-muconate was required with CatM(R156H) to activate unusually high benA expression. Thus, induction by cis,cis-muconate depends on both the sequence of CatM and the promoter. A point mutation at position -40 of the benA promoter enhanced CatM-activated gene expression and altered regulation by CatM(R156H). BenM and CatM bound to the same locations on ben region DNA. The frequency with which spontaneous mutations allow CatM to substitute for BenM might predict that one regulator would be sufficient for controlling benzoate consumption. This prediction is discussed in light of current and previous studies of the BenM-CatM regulon.
两种LysR型转录调节因子BenM和CatM控制着土壤细菌鲍氏不动杆菌ADP1对苯甲酸的消耗。这些同源物在多个基因的表达中发挥重叠作用。本研究聚焦于启动苯甲酸分解代谢的benABCDE操纵子。在此位点，BenM和CatM各自响应分解代谢物顺，顺-粘康酸激活转录。BenM而非CatM还对苯甲酸作为效应物作出响应。仅由CatM进行调节不足以支持以苯甲酸作为唯一碳源的生长。然而，三个点突变独立地增加了CatM激活的benA转录，并使得在没有BenM的情况下能够利用苯甲酸生长。两个突变产生了在303个氨基酸残基的CatM中有一个氨基酸变化的变体，即CatM(V158M)和CatM(R156H)。这些取代对benA的调节与对catB的调节不同，catB是另一个参与苯甲酸分解代谢且受CatM调节的基因。与CatM相比，CatM(V158M)增加了benA的顺，顺-粘康酸依赖性转录，但降低了catB的转录。与CatM相比，CatM(R156H)增加了catB的效应物非依赖性表达。相反，需要顺，顺-粘康酸与CatM(R156H)共同作用以激活异常高水平的benA表达。因此，顺，顺-粘康酸的诱导取决于CatM的序列和启动子。benA启动子-40位的一个点突变增强了CatM激活的基因表达，并改变了CatM(R156H)的调节作用。BenM和CatM与ben区域DNA上的相同位置结合。自发突变使CatM能够替代BenM的频率可能预示着一个调节因子就足以控制苯甲酸的消耗。根据对BenM-CatM调控子的当前和以往研究对这一预测进行了讨论。
