Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA.
UT MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA.
RNA. 2024 Nov 18;30(12):1634-1645. doi: 10.1261/rna.080210.124.
Eukaryotic genomes typically encode one member of the DXO/Dxo1/Rai1 family of enzymes, which can hydrolyze the 5' ends of RNAs with a variety of structures that deviate from the canonical GpppN. In contrast, the genome encodes two family members and the second copy, Dxo1, is a distributive 5' exoribonuclease that is required for the final maturation of the 5' end of 25S rRNA from a 25S' precursor. Here we show that this 25S rRNA maturation function is not conserved across kingdoms, but arose in the budding yeasts. Interestingly, the origin of 25S processing capacity coincides with the duplication of this gene, and this capacity is absent in the nonduplicated genes. Strikingly, two different clades of budding yeasts have undergone parallel evolution: Both duplicated their DXO/Dxo1/Rai1 gene, and in both cases, one copy gained the 25S processing function. This was accompanied by many parallel sequence changes, a remarkable case of reproducible neofunctionalization.
真核生物基因组通常编码一种 DXO/Dxo1/Rai1 酶家族的成员，该酶家族能够水解具有各种结构的 RNA 5'端，这些结构偏离了典型的 GpppN。相比之下，基因组编码两个家族成员，第二个拷贝 Dxo1 是一种分布性的 5'外切核糖核酸酶，对于 25S rRNA 5'端从 25S'前体的最终成熟是必需的。在这里，我们表明这种 25S rRNA 成熟功能在不同的生物界中并不保守，而是在出芽酵母中出现的。有趣的是，25S 加工能力的起源与该基因的复制相吻合，而在未复制的基因中则不存在这种能力。引人注目的是，两个不同的出芽酵母分支经历了平行进化：它们都复制了其 DXO/Dxo1/Rai1 基因，在这两种情况下，一个拷贝获得了 25S 加工功能。这伴随着许多平行的序列变化，是一个显著的可重复的新功能化案例。
