Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
Open Biol. 2012 Apr;2(4):120033. doi: 10.1098/rsob.120033.
The trypanosome genome is characterized by RNA polymerase II-driven polycistronic transcription of protein-coding genes. Ten to hundreds of genes are co-transcribed from a single promoter; thus, selective regulation of individual genes via initiation is impossible. However, selective responses to external stimuli occur and post-transcriptional mechanisms are thought to account for all temporal gene expression patterns. We show that genes encoding mRNAs that are differentially regulated during the heat-shock response are selectively positioned in polycistronic transcription units; downregulated genes are close to transcription initiation sites and upregulated genes are distant. We demonstrate that the position of a reporter gene within a transcription unit is sufficient to reproduce this effect. Analysis of gene ontology annotations reveals that positional bias is not restricted to stress-response genes and that there is a genome-wide organization based on proximity to transcription initiation sites. Furthermore, we show that the relative abundance of mRNAs at different time points in the cell division cycle is dependent on the location of the corresponding genes to transcription initiation sites. This work provides evidence that the genome in trypanosomes is organized to facilitate co-coordinated temporal control of gene expression in the absence of selective promoters.
锥虫基因组的特征是 RNA 聚合酶 II 驱动的蛋白质编码基因的多顺反子转录。十个到数百个基因从单个启动子共同转录；因此，通过起始对单个基因进行选择性调节是不可能的。然而，会发生选择性的对外界刺激的反应，并且认为转录后机制解释了所有的时间基因表达模式。我们表明，在热休克反应期间差异调控的编码 mRNA 的基因选择性地定位在多顺反子转录单元中；下调基因靠近转录起始位点，上调基因远离转录起始位点。我们证明，报告基因在转录单元中的位置足以重现这种效果。对基因本体注释的分析表明，位置偏向不仅限于应激反应基因，而且基于与转录起始位点的接近程度存在全基因组组织。此外，我们表明细胞分裂周期中不同时间点的 mRNA 的相对丰度取决于相应基因相对于转录起始位点的位置。这项工作提供了证据表明，在不存在选择性启动子的情况下，锥虫的基因组组织有利于协调时间控制基因表达。
