Transcriptional organization of the large and the small ATP synthase operons, atpI/H/F/A and atpB/E, in Arabidopsis thaliana chloroplasts
Transcriptional organization of the large and the small ATP synthase operons, atpI/H/F/A and atpB/E, in Arabidopsis thaliana chloroplasts
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DOI：
10.1007/s11103-012-9910-5
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发表时间：
2012-06-01
影响因子：
5.1
通讯作者：
Merendino, Livia
中科院分区：
文献类型：
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作者：
Ghulam, Mustafa Malik;Zghidi-Abouzid, Ouafa;Merendino, Livia
三磷酸腺苷合成酶是细菌和真核生物细胞器中普遍存在的一种酶。它在光合作用和呼吸过程中是必不可少的，它通过跨膜的质子运输将电化学质子梯度转化为ATP能量。在中，编码ATP合成酶亚基的基因被归类在同一个转录单元中，而在高等植物中，叶绿体基因被组织成一个大的()和一个小的()操纵子。通过模式植物，我们研究了在叶绿体中进化的策略，以克服基因簇的物理分离并协调其转录。我们证明了两个操纵子中所有被识别的启动子都是PEP依赖的，并且需要西格玛因子来进行特定的识别。我们的结果表明，这两个操纵子的转录至少由一个共同因子启动，即基本SIG2因子。我们的数据表明，SIG3和SIG6还分别参与了大操纵子和小操纵子的转录启动。我们认为SIG2可能是负责协调叶绿体基因基础转录的因子，而SIG3和SIG6可能在生理和环境条件下调节叶绿体的表达。然而，我们观察到，在sigma突变体(和)中，特定启动子的识别缺陷在很大程度上被mRNA的稳定和/或其他沉默的启动子的激活所平衡，这表明操纵子表达的限速步骤大多是转录后的。
The ATP synthase is a ubiquitous enzyme which is found in bacteria and eukaryotic organelles. It is essential in the photosynthetic and respiratory processes, by transforming the electrochemical proton gradient into ATP energy via proton transport across the membranes. In , the genes coding for the subunits of the ATP synthase enzyme are grouped in the same transcriptional unit, while in higher plants the plastid genes are organized into a large () and a small () operon. By using the model plant , we have investigated the strategy evolved in chloroplasts to overcome the physical separation of the gene clusters and to coordinate their transcription. We show that all the identified promoters in the two operons are PEP dependent and require sigma factors for specific recognition. Our results indicate that transcription of the two operons is initiated by at least one common factor, the essential SIG2 factor. Our data show that SIG3 and SIG6 also participate in transcription initiation of the large and the small operon, respectively. We propose that SIG2 might be the factor responsible for coordinating the basal transcription of the plastid genes and that SIG3 and SIG6 might serve to modulate plastid expression with respect to physiological and environmental conditions. However, we observe that in the sigma mutants ( and ) the deficiency in the recognition of specific promoters is largely balanced by mRNA stabilization and/or by activation of otherwise silent promoters, indicating that the rate-limiting step for expression of the operons is mostly post-transcriptional.