The ciliate Euplotes deviates from the universal genetic code by translating UGA as cysteine and using UAA and UAG as the termination codon. Here, we cloned and sequenced the Cathepsin B gene of Euplotes octocarinatus (Eo‐CTSB) which containing several in‐frame stop codons throughout the coding sequence. We provide evidences, based on 3′‐RACE method and Western blot, that the Eo‐CTSB gene is actively expressed. Comparison of the derived amino acid sequence with the homologs in other eukaryotes revealed that UAA and UAG may code for glutamine in Eo‐CTSB. These findings imply an evolutionary complexity of stop codon reassignment in eukaryotes.

中文翻译：

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UAA 和 UAG 可能编码 Euplotes octocarinatus 组织蛋白酶 B 基因中的氨基酸

纤毛虫 Euplotes 通过将 UGA 翻译为半胱氨酸并使用 UAA 和 UAG 作为终止密码子来偏离通用遗传密码。在这里，我们克隆并测序了 Euplotes octocarinatus (Eo-CTSB) 的组织蛋白酶 B 基因，该基因在整个编码序列中包含几个框内终止密码子。我们提供了基于 3'-RACE 方法和蛋白质印迹的证据，证明 Eo-CTSB 基因被积极表达。将衍生的氨基酸序列与其他真核生物的同源物进行比较，发现 UAA 和 UAG 可能编码 Eo-CTSB 中的谷氨酰胺。这些发现意味着真核生物中终止密码子重新分配的进化复杂性。