Schembri M A, Olsen P B, Klemm P
Department of Microbiology, Technical University of Denmark, Lyngby.
Mol Gen Genet. 1998 Aug;259(3):336-44. doi: 10.1007/s004380050820.
Phase variation of type 1 fimbriation in Escherichia coli is associated with the inversion of a 314-bp DNA element, positioned proximal to and upstream of fimA, which encodes the major type 1 fimbrial subunit. This DNA switch region contains a promoter that drives transcription of fimA only when the switch is in the ON orientation. Using chromosomal and plasmid-borne lacZ reporter cassettes, we show here how the global regulator H-NS affects the activity of the fimA promoter. In phase-locked reporter cassettes the activity of the fimA promoter was found to be enhanced in a hns-positive background, but only when the switch was in the ON orientation. Also, the number of fimbriae produced by a phase-locked ON strain was significantly higher in a hns-positive background. By means of competitive gel retardation and DNase I protection assays, H-NS binding to DNA segments adjacent to and within the phase switch region was demonstrated.
大肠杆菌中1型菌毛形成的相变与一个314 bp DNA元件的倒位有关，该元件位于编码主要1型菌毛亚基的fimA基因近端且在其上游。这个DNA开关区域包含一个启动子，只有当开关处于“开”方向时，它才驱动fimA的转录。利用染色体和质粒携带的lacZ报告盒，我们在此展示了全局调节因子H-NS如何影响fimA启动子的活性。在锁相报告盒中，发现fimA启动子的活性在hns阳性背景下增强，但仅当开关处于“开”方向时。此外，在hns阳性背景下，锁相“开”菌株产生的菌毛数量显著更高。通过竞争性凝胶阻滞和DNase I保护试验，证明了H-NS与相位开关区域相邻及内部的DNA片段结合。
