Kim Oanh Thi Phuong, Yura Kei, Go Nobuhiro, Harumoto Terue
The Division of Human Environmental Sciences, Graduate School of Human Culture, Nara Women's University, Kitauoyanishi-machi, Nara 630-8506, Japan.
Gene. 2005 Feb 14;346:277-86. doi: 10.1016/j.gene.2004.11.046. Epub 2005 Jan 4.
The genetic code of nuclear genes in some ciliates was found to differ from that of other organisms in the assignment of UGA, UAG, and UAA codons, which are normally assigned as stop codons. In some ciliate species, the universal stop codons UAA and UAG instead encode glutamine. In some other ciliates, the universal stop codon UGA appears to be translated as cysteine or tryptophan. Eukaryotic release factor 1 (eRF1) is a key protein in stop codon recognition, thus, the protein is believed to play an important role in the stop codon reassignment in ciliates. We have cloned, sequenced, and analyzed the cDNA of eRF1 from four ciliate species of three different classes: Karyorelictea (Loxodes striatus), Heterotrichea (Blepharisma musculus), and Litostomatea (Didinium nasutum, Dileptus margaritifer). Phylogenetic analysis of these eRF1s supports the hypothesis that the genetic code in ciliates has deviated independently several times from the universal genetic code, and that different ciliate eRF1s may have undergone different processes to change the codon specificity. Using computational methods, we have also suggested areas on the surface of eRF1s that are important for stop codon recognition in ciliate eRF1s.
在一些纤毛虫中，人们发现核基因的遗传密码在UGA、UAG和UAA密码子的分配上与其他生物不同，而这些密码子通常被指定为终止密码子。在一些纤毛虫物种中，通用终止密码子UAA和UAG反而编码谷氨酰胺。在其他一些纤毛虫中，通用终止密码子UGA似乎被翻译为半胱氨酸或色氨酸。真核释放因子1（eRF1）是终止密码子识别中的关键蛋白，因此，人们认为该蛋白在纤毛虫的终止密码子重新分配中发挥重要作用。我们已经克隆、测序并分析了来自三个不同类别的四种纤毛虫物种的eRF1的cDNA：核残迹纲（条纹游仆虫）、异毛纲（小家膜口虫）和膜口目（鼻滴虫、珍珠双滴虫）。对这些eRF1进行系统发育分析支持了这样的假设，即纤毛虫的遗传密码已经多次独立于通用遗传密码发生偏离，并且不同的纤毛虫eRF1可能经历了不同的过程来改变密码子特异性。通过计算方法，我们还指出了eRF1表面对于纤毛虫eRF1识别终止密码子很重要的区域。
