Pinaud S, Mirkovitch J
Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, Epalinges, CH-1066, Switzerland.
J Mol Biol. 1998 Jul 31;280(5):785-98. doi: 10.1006/jmbi.1998.1905.
The molecular mechanisms underlying transcription elongation and their role in gene regulation are poorly characterized in eukaryotes. A number of genes, however, have been proposed to be regulated at the level of transcription elongation, including c-myc, c-fos and c-myb. Here, we analyze the control of transcription elongation at the mouse c-fos gene at the nucleotide level in intact cells. We find that RNA polymerases are engaged in the promoter-proximal part of the gene in the absence of gene activation signals and mRNA synthesis. Importantly, we determine that the engaged RNA polymerases originate from a continuous initiation of transcription which, in the absence of gene activation signals, terminate close to the promoter. We also observe that the c-fos gene presents an active chromatin conformation, with the promoter and upstream regulatory sequences constitutively occupied by proteins, accounting for the continuous initiation of RNA polymerase complexes. We propose that activation of c-fos gene expression results primarily from the assembly of elongation-competent RNA polymerases that can transcribe the complete gene. Our results suggest that the engaged RNA polymerases found downstream of a number of other eukaryotic promoters may be associated with transcription termination of elongation-incompetent polymerases in the absence of activating signals.
在真核生物中，转录延伸的分子机制及其在基因调控中的作用尚未得到充分阐明。然而，已有许多基因被认为在转录延伸水平受到调控，包括c-myc、c-fos和c-myb。在此，我们在完整细胞中从核苷酸水平分析了小鼠c-fos基因转录延伸的调控。我们发现，在没有基因激活信号和mRNA合成的情况下，RNA聚合酶结合在基因启动子近端区域。重要的是，我们确定这些结合的RNA聚合酶源自转录的持续起始，在没有基因激活信号时，转录在靠近启动子的位置终止。我们还观察到，c-fos基因呈现出活跃的染色质构象，启动子和上游调控序列持续被蛋白质占据，这解释了RNA聚合酶复合物的持续起始。我们提出，c-fos基因表达的激活主要源于能够转录完整基因的具有延伸能力的RNA聚合酶的组装。我们的结果表明，在许多其他真核生物启动子下游发现的结合RNA聚合酶可能与在没有激活信号时延伸能力不足的聚合酶的转录终止有关。
