Braaten B A, Nou X, Kaltenbach L S, Low D A
Department of Pathology, University of Utah Health Sciences Center, Salt Lake City 84132.
Cell. 1994 Feb 11;76(3):577-88. doi: 10.1016/0092-8674(94)90120-1.
We have examined the roles of pap DNA methylation patterns in the regulation of the switch between phase ON and OFF pyelonephritis-associated pili (Pap) expression states in E. coli. Two Dam methyltransferase sites, GATC1028 and GATC1130, were shown previously to be differentially methylated in phase ON versus phase OFF cells. In work presented here, these sites were mutated so that they could not be methylated, and the effects of these mutations on Pap phase variation were examined. Our results show that methylation of GATC1028 blocks formation of the ON state by inhibiting the binding of Lrp and PapI regulatory proteins to this site. Conversely, methylation of GATC1130 is required for the ON state. Evidence indicates that this occurs by the inhibition of binding of Lrp to sites overlapping the pilin promoter. A model describing how the transition between the phase ON and OFF methylation states might occur is presented.
我们研究了大肠杆菌中肾盂肾炎相关菌毛（Pap）DNA甲基化模式在调控Pap表达状态从开启相到关闭相转换过程中的作用。先前已表明，两个Dam甲基转移酶位点GATC1028和GATC1130在开启相细胞与关闭相细胞中存在差异甲基化。在本文展示的研究中，对这些位点进行了突变，使其无法被甲基化，并研究了这些突变对Pap相变异的影响。我们的结果表明，GATC1028的甲基化通过抑制Lrp和PapI调节蛋白与该位点的结合来阻止开启状态的形成。相反，开启状态需要GATC1130的甲基化。有证据表明，这是通过抑制Lrp与菌毛蛋白启动子重叠位点的结合而发生的。本文还提出了一个描述开启相和关闭相甲基化状态之间转换可能如何发生的模型。
