Slomovic Shimyn, Portnoy Victoria, Yehudai-Resheff Shlomit, Bronshtein Ela, Schuster Gadi
Department of Biology, Technion - Israel Institute of Technology, Haifa, Israel.
Biochim Biophys Acta. 2008 Apr;1779(4):247-55. doi: 10.1016/j.bbagrm.2007.12.004. Epub 2007 Dec 15.
The addition of poly(A)-tails to RNA is a phenomenon common to almost all organisms. Not only homopolymeric poly(A)-tails, comprised exclusively of adenosines, but also heteropolymeric poly(A)-rich extensions, which include the other three nucleotides as well, have been observed in bacteria, archaea, chloroplasts, and human cells. Polynucleotide phosphorylase (PNPase) and the archaeal exosome, which bear strong similarities to one another, both functionally and structurally, were found to polymerize the heteropolymeric tails in bacteria, spinach chloroplasts, and archaea. As phosphorylases, these enzymes use diphosphate nucleotides as substrates and can reversibly polymerize or degrade RNA, depending on the relative concentrations of nucleotides and inorganic phosphate. A possible scenario, illustrating the evolution of RNA polyadenylation and its related functions, is presented, in which PNPase (or the archaeal exosome) was the first polyadenylating enzyme to evolve and the heteropolymeric tails that it produced, functioned in a polyadenylation-stimulated RNA degradation pathway. Only at a later stage in evolution, did the poly(A)-polymerases that use only ATP as a substrate, hence producing homopolymeric adenosine extensions, arise. Following the appearance of homopolymeric tails, a new role for polyadenylation evolved; RNA stability. This was accomplished by utilizing stable poly(A)-tails associated with the mature 3' ends of transcripts. Today, stable polyadenylation coexists with unstable heteropolymeric and homopolymeric tails. Therefore, the heteropolymeric poly(A)-rich tails, observed in bacteria, organelles, archaea, and human cells, represent an ancestral stage in the evolution of polyadenylation.
在RNA上添加聚腺苷酸尾是几乎所有生物体中都存在的现象。不仅在细菌、古细菌、叶绿体和人类细胞中观察到了仅由腺苷组成的同聚物聚腺苷酸尾，还观察到了富含聚腺苷酸的异聚物延伸，其中也包括其他三种核苷酸。发现多核苷酸磷酸化酶（PNPase）和古细菌外切体在功能和结构上彼此非常相似，它们在细菌、菠菜叶绿体和古细菌中都能使异聚物尾聚合。作为磷酸化酶，这些酶以二磷酸核苷酸为底物，并且根据核苷酸和无机磷酸的相对浓度，可以可逆地聚合或降解RNA。本文提出了一种可能的情况，用以说明RNA聚腺苷酸化及其相关功能的进化，其中PNPase（或古细菌外切体）是最早进化的聚腺苷酸化酶，它产生的异聚物尾在聚腺苷酸化刺激的RNA降解途径中发挥作用。只有在进化的后期，才出现了仅以ATP为底物从而产生同聚物腺苷延伸的聚腺苷酸聚合酶。同聚物尾出现后，聚腺苷酸化进化出了新的作用；即RNA稳定性。这是通过利用与转录本成熟3'端相关的稳定聚腺苷酸尾来实现的。如今，稳定的聚腺苷酸化与不稳定的异聚物和同聚物尾共存。因此，在细菌、细胞器、古细菌和人类细胞中观察到的富含聚腺苷酸的异聚物尾代表了聚腺苷酸化进化的一个祖先阶段。
