Berger Michael, Gerganova Veneta, Berger Petya, Rapiteanu Radu, Lisicovas Viktoras, Dobrindt Ulrich
Institut für Hygiene, University Münster, Mendelstraße 7, 48149 Münster, Germany.
School of Engineering and Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany.
Sci Rep. 2016 Aug 22;6:31512. doi: 10.1038/srep31512.
The extent to which chromosomal gene position in prokaryotes affects local gene expression remains an open question. Several studies have shown that chromosomal re-positioning of bacterial transcription units does not alter their expression pattern, except for a general decrease in gene expression levels from chromosomal origin to terminus proximal positions, which is believed to result from gene dosage effects. Surprisingly, the question as to whether this chromosomal context independence is a cis encoded property of a bacterial transcription unit, or if position independence is a property conferred by factors acting in trans, has not been addressed so far. For this purpose, we established a genetic test system assessing the chromosomal positioning effects by means of identical promoter-fluorescent reporter gene fusions inserted equidistantly from OriC into both chromosomal replichores of Escherichia coli K-12. Our investigations of the reporter activities in mutant cells lacking the conserved nucleoid associated protein HU uncovered various drastic chromosomal positional effects on gene transcription. In addition we present evidence that these positional effects are caused by transcriptional activity nearby the insertion site of our reporter modules. We therefore suggest that the nucleoid-associated protein HU is functionally insulating transcription units, most likely by constraining transcription induced DNA supercoiling.
原核生物中染色体基因位置对局部基因表达的影响程度仍是一个悬而未决的问题。多项研究表明，细菌转录单元的染色体重新定位不会改变其表达模式，除了从染色体起点到近端位置的基因表达水平普遍下降，这被认为是由基因剂量效应导致的。令人惊讶的是，关于这种染色体背景独立性是细菌转录单元的顺式编码特性，还是位置独立性是由反式作用因子赋予的特性这一问题，迄今为止尚未得到解决。为此，我们建立了一个遗传测试系统，通过将相同的启动子 - 荧光报告基因融合体从OriC等距离插入大肠杆菌K - 12的两个染色体复制子中来评估染色体定位效应。我们对缺乏保守类核相关蛋白HU的突变细胞中报告基因活性的研究揭示了对基因转录的各种显著染色体位置效应。此外，我们提供证据表明这些位置效应是由报告模块插入位点附近的转录活性引起的。因此，我们认为类核相关蛋白HU在功能上隔离转录单元，很可能是通过限制转录诱导的DNA超螺旋来实现的。
