Sánchez-Silva Rocío, Villalobo Eduardo, Morin Loïc, Torres Antonio
Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, 41012 Sevilla, Spain.
Curr Biol. 2003 Mar 4;13(5):442-7. doi: 10.1016/s0960-9822(03)00126-x.
Deviant genetic codes reported in ciliates share the same feature: one (UGA) or two (UAR) of the three canonical stop codons are translated into one particular amino acid. In many genera, such as Oxytricha, Paramecium, and Tetrahymena, UAR codons are translated into glutamine. UGA is translated into cysteine in Euplotes or into tryptophan in Colpoda inflata and Blepharisma americanum. Here, we show that three peritrich species (Vorticella microstoma, Opisthonecta henneguyi, and Opisthonecta matiensis) translate UAA into glutamate and that at least UAA in O. matiensis is decoded through a mutant suppressor-like tRNA. This kind of genetic code has never been reported for any living organism. Phylogenetic analysis with alpha-tubulin sequences corroborates that peritrichs, peniculines (Paramecium), and hymenostomates (Tetrahymena) form a monophyletic group (class Oligohymenophorea). The differential translation (glu/gln) of UAR codons, the monophyly of the Oligohymenophorea, and the common evolutionary origin of glutamate and glutamine suggest that deviant genetic codes of present-day oligohymenophoreans could have the same origin.
三个标准终止密码子中的一个（UGA）或两个（UAR）被翻译成一种特定的氨基酸。在许多属中，如尖毛虫属、草履虫属和四膜虫属，UAR密码子被翻译成谷氨酰胺。在游仆虫属中UGA被翻译成半胱氨酸，在膨胀肾形虫和美洲颈草履虫中UGA被翻译成色氨酸。在这里，我们表明三种缘毛类物种（小口钟虫、亨氏后口虫和马氏后口虫）将UAA翻译成谷氨酸，并且至少马氏后口虫中的UAA是通过一种类似突变抑制tRNA解码的。这种遗传密码在任何生物体中都从未被报道过。用α-微管蛋白序列进行的系统发育分析证实，缘毛类、笔毛虫类（草履虫）和膜口类（四膜虫）形成一个单系类群（寡膜纲）。UAR密码子的差异翻译（glu/gln）、寡膜纲的单系性以及谷氨酸和谷氨酰胺的共同进化起源表明，当今寡膜纲生物的异常遗传密码可能有相同的起源。
