Whitworth David E, Bryan Samantha J, Berry Andrew E, McGowan Simon J, Hodgson David A
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
J Bacteriol. 2004 Dec;186(23):7836-46. doi: 10.1128/JB.186.23.7836-7846.2004.
In Myxococcus xanthus photoprotective carotenoids are produced in response to illumination due to regulated expression of carotenoid biosynthesis genes at two loci. Induction of the carotenogenesis regulon is dependent on expression of the carQRS operon. The first gene product of the operon, CarQ, is a sigma factor belonging to the ECF family and is responsible for light-dependent initiation of transcription at the carQRS promoter. We defined the minimal carQRS promoter as a 145-bp fragment of DNA upstream of the carQRS transcriptional start site, which includes the promoter for a divergent gene, gufA. In order to elucidate regions with the promoter required for activity, point mutations were introduced into the carQRS promoter between positions -151 and 6. While most sequence changes abolished carQRS promoter activity, two changes enhanced promoter activity and two changes caused the mutant promoter to become constitutive and independent of CarQ. The promoter-null point mutations and 6-bp deletion mutations implied that the carQRS promoter requires a functional gufA promoter for transcriptional activity and vice versa. By mapping the extent of the promoter region, identifying sequences important for promoter activity, and highlighting potential topological effects, we provide a foundation for further analysis of the carQRS promoter.
在黄色粘球菌中，由于类胡萝卜素生物合成基因在两个位点的表达受到调控，光保护类胡萝卜素是在光照响应下产生的。类胡萝卜素生成调节子的诱导依赖于carQRS操纵子的表达。该操纵子的第一个基因产物CarQ是一种属于ECF家族的σ因子，负责在carQRS启动子处进行光依赖性转录起始。我们将最小的carQRS启动子定义为carQRS转录起始位点上游145 bp的DNA片段，其中包括一个 divergent基因gufA的启动子。为了阐明启动子活性所需的区域，在-151和6位之间的carQRS启动子中引入了点突变。虽然大多数序列变化消除了carQRS启动子活性，但有两个变化增强了启动子活性，还有两个变化导致突变启动子变得组成型且不依赖于CarQ。启动子缺失点突变和6 bp缺失突变表明，carQRS启动子需要一个功能性的gufA启动子来进行转录活性，反之亦然。通过绘制启动子区域的范围、确定对启动子活性重要的序列以及突出潜在的拓扑效应，我们为进一步分析carQRS启动子提供了基础。
