Beauregard Arthur, Chalamcharla Venkata R, Piazza Carol Lyn, Belfort Marlene, Coros Colin J
Molecular Genetics Program, Wadsworth Center, New York State Department of Health, Center for Medical Sciences, 150 New Scotland Avenue, Albany, NY 12208, USA.
Mol Microbiol. 2006 Nov;62(3):709-22. doi: 10.1111/j.1365-2958.2006.05419.x. Epub 2006 Sep 27.
Group II introns are mobile genetic elements that invade their cognate intron-minus alleles via an RNA intermediate, in a process known as retrohoming. They can also retrotranspose to ectopic sites at low frequency. In Escherichia coli, retrotransposition of the lactococcal group II intron, Ll.LtrB, occurs preferentially within the Ori and Ter macrodomains of the E. coli chromosome. These macrodomains migrate towards the poles of the cell, where the intron-encoded protein, LtrA, localizes. Here we investigate whether alteration of nucleoid condensation, chromosome partitioning and replication affect retrotransposition frequencies, as well as bipolar localization of the Ll.LtrB intron integration and LtrA distribution in E. coli. We thus examined these properties in the absence of the nucleoid-associated proteins H-NS, StpA and MukB, in variants of partitioning functions including the centromere-like sequence migS and the actin homologue MreB, as well as in the replication mutants DeltaoriC, seqA, tus and topoIV (ts). Although there were some dramatic fluctuations in retrotransposition levels in these hosts, bipolar localization of integration events was maintained. LtrA was consistently found in nucleoid-free regions, with its localization to the cellular poles being largely preserved in these hosts. Together, these results suggest that bipolar localization of group II intron retrotransposition results from the residence of the intron-encoded protein at the poles of the cell.
II类内含子是可移动的遗传元件，它们通过RNA中间体侵入其同源的无内含子等位基因，这一过程称为反转录归巢。它们也能以低频率反转录转座到异位位点。在大肠杆菌中，乳球菌II类内含子Ll.LtrB的反转录转座优先发生在大肠杆菌染色体的Ori和Ter宏结构域内。这些宏结构域向细胞两极迁移，内含子编码的蛋白LtrA定位于此。在这里，我们研究了类核凝聚、染色体分配和复制的改变是否会影响反转录转座频率，以及Ll.LtrB内含子整合的双极定位和LtrA在大肠杆菌中的分布。因此，我们在缺乏类核相关蛋白H-NS、StpA和MukB的情况下，在包括着丝粒样序列migS和肌动蛋白同源物MreB在内的分配功能变体中，以及在复制突变体DeltaoriC、seqA、tus和拓扑异构酶IV（ts）中检查了这些特性。尽管这些宿主中的反转录转座水平存在一些剧烈波动，但整合事件的双极定位得以维持。LtrA始终存在于无类核区域，其在细胞两极的定位在这些宿主中基本保持不变。总之，这些结果表明II类内含子反转录转座的双极定位是由内含子编码蛋白在细胞两极的定位所致。
