Nascent ribosomal 60S subunits undergo the last maturation steps in the cytoplasm. The last one involves removing the anti-association factor eIF6 from the 60S ribosomal surface by the joint action of the Elongation Factor-like 1 (EFL1) GTPase and the SBDS protein. Herein, we studied the evolutionary relationship of the EFL1 and EF-2 protein families and the functional conservation within EFL1 orthologues. Phylogenetic analysis demonstrated that the EFL1 proteins are exclusive of eukaryotes and share an evolutionary origin with the EF-2 and EF-G protein families. EFL1 proteins originated by gene duplication from the EF-2 proteins and specialized in ribosome maturation while the latter retained their function in translation. Some organisms have more than one EFL1 protein resulting from alternative splicing, while others are encoded in different genes originated by gene duplication. However, the function of these alternative EFL1 proteins is still unknown. We performed GTPase activity and complementation assays to study the functional conservation of EFL1 homologs alone and together with their SBDS counterparts. None of the orthologues or cross-species combinations could replace the function of the corresponding yeast EFL1•SBDS binomial. The complementation of SBDS interspecies chimeras indicates that domain 2 is vital for its function together with EFL1 and the 60S subunit. The results suggest a functional species-specificity and possible co-evolution between EFL1, SBDS, and the 60S ribosomal subunit. These findings set the basis for further studies directed to understand the molecular evolution of these proteins and their impact on ribosome biogenesis and disease.

新生核糖体 60S 亚基在细胞质中经历最后的成熟步骤。最后一个涉及通过延伸因子样 1 (EFL1) GTPase 和 SBDS 蛋白的共同作用从 60S 核糖体表面去除抗结合因子 eIF6。在此，我们研究了 EFL1 和 EF-2 蛋白家族的进化关系以及 EFL1 直向同源物内的功能保守性。系统发育分析表明，EFL1 蛋白不包括真核生物，并且与 EF-2 和 EF-G 蛋白家族共享进化起源。EFL1 蛋白源自 EF-2 蛋白的基因复制，专门用于核糖体成熟，而后者保留其翻译功能。一些生物体具有由选择性剪接产生的不止一种 EFL1 蛋白，而另一些则由基因复制产生的不同基因编码。然而，这些替代 EFL1 蛋白的功能仍然未知。我们进行了 GTPase 活性和互补测定，以研究 EFL1 同源物单独及其与其 SBDS 对应物的功能保守性。直向同源物或跨物种组合都不能替代相应酵母 EFL1•SBDS 二项式的功能。SBDS 种间嵌合体的互补表明域 2 与 EFL1 和 60S 亚基一起对其功能至关重要。结果表明 EFL1、SBDS 和 60S 核糖体亚基之间存在功能性物种特异性和可能的​​共同进化。