Berg K L, Squires C, Squires C L
Department of Biological Sciences, Columbia University, New York, NY 10027.
J Mol Biol. 1989 Oct 5;209(3):345-58. doi: 10.1016/0022-2836(89)90002-8.
All Escherichia coli rrn operons show a common motif in which anti-terminator box B-box A sequences occur twice, first in the leader and again in the 16 S-23 S spacer. In this study we have analyzed several aspects of rrn anti-termination by leader and spacer anti-terminator sequences. Using DNA synthesis and a plasmid test system, we incorporated random changes into the leader anti-terminator region and examined these mutations for their ability to read through a strong terminator. We also examined anti-termination by synthetic box A and by rrn spacer region sequences. Information derived from these experiments was used to search the rrn sequences of other micro-organisms for possible anti-termination features. Our principal conclusions were that: (1) box A was sufficient for terminator readthrough; (2) we could show no positive requirement for box B in our test system; (3) many of the negative anti-terminator mutations caused a promoter up-effect in the absence of a terminator; (4) the search of rrn operons from other micro-organisms revealed that anti-terminator-like box B-box A sequences exist in leader and spacer regions of both eubacteria and archaebacteria. The frequent occurrence of this pattern suggested that the E. coli rrn anti-termination motif is widespread in nature and has been conserved in microbial evolution.
所有大肠杆菌rrn操纵子都显示出一个共同的基序，其中抗终止子的B框-A框序列出现两次，第一次在先导区，第二次在16S-23S间隔区。在本研究中，我们分析了先导区和间隔区抗终止子序列在rrn抗终止方面的几个方面。利用DNA合成和质粒测试系统，我们在先导区抗终止子区域引入随机变化，并检测这些突变体通读强终止子的能力。我们还检测了合成的A框和rrn间隔区序列的抗终止作用。从这些实验中获得的信息用于搜索其他微生物的rrn序列，以寻找可能的抗终止特征。我们的主要结论是：（1）A框足以实现终止子通读；（2）在我们的测试系统中，我们未发现对B框有正向需求；（3）许多负向抗终止子突变在没有终止子的情况下导致启动子上调效应；（4）对其他微生物rrn操纵子的搜索表明，真细菌和古细菌的先导区和间隔区都存在类似抗终止子的B框-A框序列。这种模式的频繁出现表明，大肠杆菌rrn抗终止基序在自然界中广泛存在，并且在微生物进化过程中得以保留。
