Stephens C M, Shapiro L
Department of Developmental Biology, Beckman Center, Stanford University, California 94305.
Mol Microbiol. 1993 Sep;9(6):1169-79. doi: 10.1111/j.1365-2958.1993.tb01246.x.
Transcription of flagellar genes in Caulobacter crecentus is programmed to occur during the predivisional stage of the cell cycle. The mechanism of activation of Class II flagellar genes, the highest identified genes in the Caulobacter flagellar hierarchy, is unknown. As a step toward understanding this process, we have defined cis-acting sequences necessary for expression of a Class II flagellar operon, fliLM. Deletion analysis indicated that a 55 bp DNA fragment was sufficient for normal, temporally regulated promoter activity. Transcription from this promoter-containing fragment was severely reduced when chromosomal DNA replication was inhibited. Extensive mutational analysis of the promoter region from -42 to -5 identified functionally important nucleotides at -36 and -35, between -29 and -22, and at -12, which correlates well with sequences conserved between fliLM and the analogous regions of two other Class II flagellar operons. The promoter sequence does not resemble that recognized by any known bacterial sigma factor. Models for regulation of Caulobacter early flagellar promoters are discussed in which RNA polymerase containing a novel sigma subunit interacts with an activation factor bound to the central region of the promoter.
新月柄杆菌中鞭毛基因的转录被安排在细胞周期的前分裂阶段进行。II类鞭毛基因是新月柄杆菌鞭毛层级中已确定的最高级基因，其激活机制尚不清楚。作为理解这一过程的第一步，我们已经确定了II类鞭毛操纵子fliLM表达所必需的顺式作用序列。缺失分析表明，一个55 bp的DNA片段足以实现正常的、受时间调控的启动子活性。当染色体DNA复制受到抑制时，来自这个含启动子片段的转录会严重减少。对-42至-5的启动子区域进行广泛的突变分析，确定了-36和-35、-29至-22之间以及-12处功能重要的核苷酸，这与fliLM和其他两个II类鞭毛操纵子的类似区域之间保守的序列高度相关。该启动子序列与任何已知细菌sigma因子所识别的序列都不相似。文中讨论了新月柄杆菌早期鞭毛启动子的调控模型，其中含有新型sigma亚基的RNA聚合酶与结合在启动子中心区域的激活因子相互作用。
