Environmental PCR survey to determine the distribution of a non-canonical genetic code in uncultivable oxymonads
Environmental PCR survey to determine the distribution of a non-canonical genetic code in uncultivable oxymonads
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DOI：
10.1111/j.1462-2920.2007.01430.x
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发表时间：
2008-01-01
影响因子：
5.1
通讯作者：
Keeling, Patrick J.
中科院分区：
文献类型：
--
作者：
de Koning, Audrey P.;Noble, Geoffrey P.;Keeling, Patrick J.
通用遗传密码在大多数生命系统中是保守的，但在几种真核生物（包括氧化单胞菌原生生物）中进化出了TAA和TAG编码谷氨酰胺的非规范密码。大多数氧化单胞菌是不可培养的，所以环境RT-PCR和PCR被用来检测这一罕见性状的分布。共253个独特的分离物的4个蛋白质编码基因进行了采样从后肠社区的蟑螂，Cryptocercus punctulatus，一个环境中丰富的多样性，从两个5个亚组的oxymonad，saccinobaculids和polymastigids。发现四种α-微管蛋白具有非典型的谷氨酰胺密码子。环境RACE证实，这些基因和相关基因仅使用TGA作为终止密码子，正如非经典密码所预期的那样，而其他基因使用TAA或TAG作为终止密码子，正如通用密码所预期的那样。我们的特点是α-微管蛋白从手动分离的Saccinobaculus ambloaxostylus，确认它使用的通用代码，并建议，通过消除，非规范的代码是由一个polymastigid使用。HSP 90和EF-1 α基因也显示了环境序列分为两个不同的群体，并与以前的假设，即多鞭毛虫和Streblomastix是密切相关的。总体而言，我们建议，非典型的遗传密码出现在一个共同的祖先Streblomastix和一个亚组的polymastigids。
The universal genetic code is conserved throughout most living systems, but a non-canonical code where TAA and TAG encode glutamine has evolved in several eukaryotes, including oxymonad protists. Most oxymonads are uncultivable, so environmental RT-PCR and PCR was used to examine the distribution of this rare character. A total of 253 unique isolates of four protein-coding genes were sampled from the hindgut community of the cockroach, Cryptocercus punctulatus, an environment rich in diversity from two of the five subgroups of oxymonad, saccinobaculids and polymastigids. Four alpha-tubulins were found with non-canonical glutamine codons. Environmental RACE confirmed that these and related genes used only TGA as stop codons, as expected for the non-canonical code, whereas other genes used TAA or TAG as stop codons, as expected for the universal code. We characterized alpha-tubulin from manually isolated Saccinobaculus ambloaxostylus, confirming it uses the universal code and suggesting, by elimination, that the non-canonical code is used by a polymastigid. HSP90 and EF-1 alpha phylogenies also showed environmental sequences falling into two distinct groups, and are generally consistent with previous hypotheses that polymastigids and Streblomastix are closely related. Overall, we propose that the non-canonical genetic code arose once in a common ancestor of Streblomastix and a subgroup of polymastigids.