Miceli C, Ballarini P, Di Giuseppe G, Valbonesi A, Luporini P
Dipartimento di Biologia Molecolare, Cellulare ed Animale Università di Camerino, Italy.
J Eukaryot Microbiol. 1994 Jul-Aug;41(4):420-7. doi: 10.1111/j.1550-7408.1994.tb06100.x.
Four different tubulin genes were identified in the somatic nucleus (macronucleus) of Euplotes focardii, a strictly cold-adapted, Antarctic ciliate: one of 1,800 bp for alpha-tubulin and three of 2,150, 1,900, and 1,600 bp, respectively, for beta-tubulin. Preliminarily analysed for restriction fragment length polymorphisms, these genes showed remarkable differences in organisation from tubulin genes of other ciliates which live in temperate areas and were analysed in parallel with E. focardii. The complete coding sequence of the 1,600 bp beta-tubulin gene was then determined and shown to contain unique structural features of potential importance for E. focardii microtubule organization and activity. Of eight unique substitutions detected, seven were concentrated in the large amino terminal domain of the molecule that directly interacts with the carboxy terminal region of alpha-tubulin for heterodimer formation. Sequence analysis of the cloned gene revealed, in addition, a potential new exception in the use of the genetic code by ciliates. A TAG codon was aligned in correspondence with Trp-21 which is strictly conserved in every tubulin sequence so far determined.
在福氏游仆虫（Euplotes focardii）的体细胞核（大核）中鉴定出了四种不同的微管蛋白基因，福氏游仆虫是一种严格适应寒冷环境的南极纤毛虫：一种1800 bp的α-微管蛋白基因，以及三种分别为2150 bp、1900 bp和1600 bp的β-微管蛋白基因。对这些基因进行了限制性片段长度多态性的初步分析，结果显示它们在结构上与生活在温带地区的其他纤毛虫的微管蛋白基因存在显著差异，并且是与福氏游仆虫平行分析的。随后确定了1600 bp的β-微管蛋白基因的完整编码序列，并发现其包含对福氏游仆虫微管组织和活性具有潜在重要性的独特结构特征。在检测到的八个独特替换中，有七个集中在分子的大氨基末端结构域，该结构域直接与α-微管蛋白的羧基末端区域相互作用以形成异二聚体。此外，对克隆基因的序列分析揭示了纤毛虫在遗传密码使用方面可能存在的一个新例外。一个TAG密码子与色氨酸-21对应排列，色氨酸-21在迄今为止确定的每个微管蛋白序列中都严格保守。
