Göransson M, Forsman K, Uhlin B E
Department of Microbiology, University of Umeå, Sweden.
Genes Dev. 1989 Jan;3(1):123-30. doi: 10.1101/gad.3.1.123.
Expression of several different pilus adhesins by Escherichia coli is subject to thermoregulation. The surface-located fimbrial structures are present during growth at 37 degrees C but are not produced by cells grown at lower temperatures, such as 25 degrees C. As a step toward understanding the molecular mechanism, we have studied the role of different cistrons of a cloned pilus adhesin gene cluster (pap) from a uropathogenic E. coli isolate. By promoter cloning, mRNA analysis, and expression of subcloned genes in trans, we have identified the papI gene as the mediator of thermoregulation at the level of pilus adhesin gene transcription. Expression of the major pilus subunit gene (papA) and several other pilus protein cistrons appeared to be dependent on stimulation by the papB and papI gene products. Constructs carrying different pap DNA regions indicated that none of the known Pap proteins acts directly as thermosensor. The chromosomal rpoH gene and RpoH sigma factor did not appear to be required for pap transcription, and the thermoregulation of pilus gene transcription must be different from that of the heat shock regulon. By overexpressing the papI gene product from an expression plasmid in trans, we could circumvent the temperature regulation and turn on production of pilus adhesin at low temperature. Our results suggest that the level of mRNA encoding the PapI activator is limiting at low growth temperatures and that thermoregulation is due to a determinant in the papI-papB intercistronic region.
大肠杆菌中几种不同菌毛黏附素的表达受温度调节。表面定位的菌毛结构在37℃生长时存在，但在较低温度（如25℃）下生长的细胞中不产生。作为了解分子机制的第一步，我们研究了来自尿路致病性大肠杆菌分离株的克隆菌毛黏附素基因簇（pap）不同顺反子的作用。通过启动子克隆、mRNA分析以及亚克隆基因的反式表达，我们确定papI基因是菌毛黏附素基因转录水平上温度调节的介导因子。主要菌毛亚基基因（papApaA）和其他几个菌毛蛋白顺反子的表达似乎依赖于papB和papI基因产物的刺激。携带不同pap DNA区域的构建体表明，已知的Pap蛋白均不直接作为温度感受器。染色体上的rpoH基因和RpoH σ因子似乎不是pap转录所必需的，菌毛基因转录的温度调节一定不同于热休克调节子的调节。通过从表达质粒反式过表达papI基因产物，我们可以规避温度调节并在低温下开启菌毛黏附素的产生。我们的结果表明，编码PapI激活剂的mRNA水平在低生长温度下是有限的，并且温度调节是由于papI - papB基因间区域的一个决定因素。
