Seligmann Hervé, Labra Antonieta
Center for Ecological and Evolutionary Synthesis, Department of Bioscience, University of Oslo, Blindern, N-0316 Oslo, Norway; National Natural History Museum Collections, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel; Department of Life Sciences, Ben Gurion University, 84105 Beer Sheva, Israel.
Center for Ecological and Evolutionary Synthesis, Department of Bioscience, University of Oslo, Blindern, N-0316 Oslo, Norway; Programa de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Casilla 70005, Santiago, Chile.
Gene. 2014 Jun 1;542(2):248-57. doi: 10.1016/j.gene.2014.02.021. Epub 2014 Feb 18.
Mitochondrial light strand DNA replication is initiated at light strand replication origins (OLs), short stem-loop hairpins formed by the heavy strand DNA. OL-like secondary structures are also formed by heavy strand DNA templating for the five tRNAs adjacent to OLs, the WANCY tRNA cluster. We tested whether natural OL absence associates with greater capacities for formation of OL-like structures by WANCY tRNA genes. Using lepidosaurian taxa (Sphenodon, lizards and amphisbaenids), we compared WANCY tRNA capacities to form OL-like structures between 248 taxa possessing an OL with 131 taxa without OL (from different families). On average, WANCY tRNA genes form more OL-like structures in the absence of a regular OL than in its presence. Formation of OL-like structures by WANCY tRNAs follows hierarchical patterns that may reduce competition between the tRNA's translational function and its secondary OL function: the rarer the tRNA's cognate amino acid, the greater the capacity to form OL-like structures. High OL-forming capacities for neighboring tRNAs are avoided. Because OL absence usually occurs in taxa with reduced genomes, increased formation of OL-like structures by WANCY tRNAs might result from selection for greater metabolic efficiency. Further analyses suggest that OL loss is one of the latest steps in genome reduction, and promotes the increase in formation of OL-like structures by WANCY tRNA genes in Lepidosauria.
线粒体轻链DNA复制起始于轻链复制起点（OLs），即由重链DNA形成的短茎环发夹结构。与OLs相邻的五个tRNA（WANCY tRNA簇）的重链DNA模板也会形成类似OL的二级结构。我们测试了天然OL缺失是否与WANCY tRNA基因形成类似OL结构的能力增强有关。利用鳞龙类分类群（楔齿蜥、蜥蜴和蚓蜥），我们比较了248个具有OL的分类群和131个没有OL的分类群（来自不同科）之间WANCY tRNA形成类似OL结构的能力。平均而言，在没有常规OL的情况下，WANCY tRNA基因形成的类似OL结构比有OL时更多。WANCY tRNA形成类似OL结构遵循分层模式，这可能会减少tRNA翻译功能与其二级OL功能之间的竞争：tRNA的同源氨基酸越稀有，形成类似OL结构的能力就越强。相邻tRNA的高OL形成能力会被避免。由于OL缺失通常发生在基因组减少的分类群中，WANCY tRNA形成类似OL结构的增加可能是由于对更高代谢效率的选择。进一步分析表明，OL丢失是基因组减少的最新步骤之一，并促进了鳞龙类中WANCY tRNA基因形成类似OL结构的增加。
