Bose Arpita, Metcalf William W
Department of Microbiology, University of Illinois at Urbana-Champaign, B103 CLSL, 601 S. Goodwin, Urbana, IL 61801, USA.
Mol Microbiol. 2008 Feb;67(3):649-61. doi: 10.1111/j.1365-2958.2007.06075.x. Epub 2007 Dec 13.
The mtaCB1, mtaCB2 and mtaCB3 operons encode isozymes of methanol methyltransferases in Methanosarcina acetivorans C2A and are among the most highly regulated genes known in Archaea. Here we identify cis and trans acting elements that affect the expression of these operons. In vivo reporter gene constructs expressed from sequentially truncated promoters show that the mRNA transcripts for these operons have large 5' untranslated regions. Regions upstream of the transcription start site (TSS) are important for induction of the mtaCB1 and mtaCB2 operons and for repression of the mtaCB3. Regions downstream of the TSS are important for expression of the mtaCB2 and mtaCB3 operons, but are dispensable for mtaCB1 expression. Proteins encoded by the MA0459 and MA0460 loci are required for induction of the mtaCB1 operon, while those encoded by MA4383, MA4397 and MA4398 are required for induction of mtaCB2. Proteins encoded by MA4397 and MA4398 are also required for methanol-specific repression of the mtaCB3 operon and, thus, are the first archaeal examples of regulatory proteins that simultaneously act in both repression and activation. We refer to these genes as methanol-specific regulators and designate MA0459, MA0460, MA4383, MA4397 and MA4398 as msrA, msrB, msrC, msrD and msrE respectively.
mtaCB1、mtaCB2和mtaCB3操纵子编码嗜乙酸甲烷八叠球菌C2A中甲醇甲基转移酶的同工酶，是古菌中已知调控程度最高的基因之一。在此，我们鉴定了影响这些操纵子表达的顺式和反式作用元件。从连续截短的启动子表达的体内报告基因构建体表明，这些操纵子的mRNA转录本具有大的5'非翻译区。转录起始位点（TSS）上游的区域对于mtaCB1和mtaCB2操纵子的诱导以及mtaCB3的抑制很重要。TSS下游的区域对于mtaCB2和mtaCB3操纵子的表达很重要，但对于mtaCB1的表达是可有可无的。MA0459和MA0460位点编码的蛋白质是mtaCB1操纵子诱导所必需的，而MA4383、MA4397和MA4398编码的蛋白质是mtaCB2诱导所必需的。MA4397和MA4398编码的蛋白质也是mtaCB3操纵子甲醇特异性抑制所必需的，因此，是同时在抑制和激活中起作用的调节蛋白的首个古菌实例。我们将这些基因称为甲醇特异性调节因子，并分别将MA0459、MA0460、MA4383、MA4397和MA4398指定为msrA、msrB、msrC、msrD和msrE。
