Swine Science and Technology Center, Gyeongnam National University of Science and Technology-GNTECH, Jinju 660-758, Korea.
Plant J. 2012 Jul;71(1):122-34. doi: 10.1111/j.1365-313X.2012.04976.x. Epub 2012 Apr 26.
The Spo0B-associated GTP-binding protein (Obg) GTPase, essential for bacterial viability, is also conserved in eukaryotes, but its primary role in eukaryotes remains unknown. Here, our functional characterization of Arabidopsis and rice obgc mutants strongly underlines the evolutionarily conserved role of eukaryotic Obgs in organellar ribosome biogenesis. The mutants exhibited a chlorotic phenotype, caused by retarded chloroplast development. A plastid DNA macroarray revealed a plastid-encoded RNA polymerase (PEP) deficiency in an obgc mutant, caused by incompleteness of the PEP complex, as its western blot exhibited reduced levels of RpoA protein, a component of PEP. Plastid rRNA profiling indicated that plastid rRNA processing is defective in obgc mutants, probably resulting in impaired ribosome biogenesis and, in turn, in reduced levels of RpoA protein. RNA co-immunoprecipitation revealed that ObgC specifically co-precipitates with 23S rRNA in vivo. These findings indicate that ObgC functions primarily in plastid ribosome biogenesis during chloroplast development. Furthermore, complementation analysis can provide new insights into the functional modes of three ObgC domains, including the Obg fold, G domain and OCT.
Spo0B 相关 GTP 结合蛋白（Obg）GTP 酶对于细菌的生存至关重要，在真核生物中也保守存在，但它在真核生物中的主要作用仍然未知。在这里，我们对拟南芥和水稻 obgc 突变体的功能特征进行了分析，强烈地强调了真核生物 Obgs 在细胞器核糖体生物发生中的进化保守作用。突变体表现出黄化表型，这是由叶绿体发育迟缓引起的。一个质体 DNA 宏阵列揭示了 obgc 突变体中质体编码 RNA 聚合酶（PEP）的缺乏，这是由于 PEP 复合物的不完整，其 Western blot 显示 RpoA 蛋白水平降低，RpoA 蛋白是 PEP 的一个组成部分。质体 rRNA 分析表明质体 rRNA 加工在 obgc 突变体中存在缺陷，可能导致核糖体生物发生受损，进而导致 RpoA 蛋白水平降低。RNA 共免疫沉淀显示 ObgC 与 23S rRNA 特异性地在体内共沉淀。这些发现表明 ObgC 主要在叶绿体发育过程中的质体核糖体生物发生中发挥作用。此外，互补分析可以为 ObgC 三个结构域（Obg 折叠结构域、G 结构域和 OCT 结构域）的功能模式提供新的见解。
