Fernández de Henestrosa Antonio R, Cuñé Jordi, Mazón Gerard, Dubbels Bradley L, Bazylinski Dennis A, Barbé Jordi
Departament Genètica i Microbiologia, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain.
J Bacteriol. 2003 Aug;185(15):4471-82. doi: 10.1128/JB.185.15.4471-4482.2003.
MC-1 is a marine, magnetotactic bacterium that is phylogenetically associated with the alpha subclass of the Proteobacteria and is the first and only magnetotactic coccus isolated in pure culture to date. By using a TBLASTN search, a lexA gene was identified in the published genome of MC-1; it was subsequently cloned, and the protein was purified to >90% purity. Results from reverse transcription-PCR analysis revealed that the MC-1 lexA gene comprises a single transcriptional unit with two open reading frames encoding proteins of unknown function and with a rumA-like gene, a homologue of the Escherichia coli umuD gene. Mobility shift assays revealed that this LexA protein specifically binds both to its own promoter and to that of the umuDC operon. However, MC-1 LexA does not bind to the promoter regions of other genes, such as recA and uvrA, that have been previously reported to be regulated by LexA in bacterial species belonging to the alpha subclass of the Proteobacteria: Site-directed mutagenesis of both the lexA and umuDC operator regions demonstrated that the sequence CCTN(10)AGG is the specific target motif for the MC-1 LexA protein.
MC-1是一种海洋趋磁细菌，在系统发育上与变形菌门的α亚类相关，是迄今为止在纯培养物中分离出的首个也是唯一的趋磁球菌。通过使用TBLASTN搜索，在已发表的MC-1基因组中鉴定出一个lexA基因；随后对其进行克隆，并将该蛋白纯化至纯度大于90%。逆转录-聚合酶链反应分析结果表明，MC-1的lexA基因包含一个单一转录单元，有两个编码功能未知蛋白质的开放阅读框，以及一个rumA样基因，它是大肠杆菌umuD基因的同源物。迁移率变动分析表明，这种LexA蛋白能特异性结合其自身启动子以及umuDC操纵子的启动子。然而，MC-1 LexA并不结合其他基因的启动子区域，比如recA和uvrA，而之前报道在属于变形菌门α亚类的细菌物种中，这些基因是受LexA调控的：对lexA和umuDC操纵基因区域进行定点诱变表明，序列CCTN(10)AGG是MC-1 LexA蛋白的特异性靶基序。
