PAK paradox:: Paramecium appear to have more K+-channel genes than humans
PAK paradox:: Paramecium appear to have more K+-channel genes than humans
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DOI：
10.1128/ec.2.4.737-745.2003
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发表时间：
2003-08-01
期刊：
影响因子：
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通讯作者：
Kung, C
中科院分区：
文献类型：
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作者：
Haynes, WJ;Ling, KY;Kung, C
K+选择性离子通道（K+通道）已在细菌、古细菌、桉树和病毒中发现。在草履虫和其他纤毛虫中，K+电流在纤毛运动中起着重要作用。我们检索并测序了7个密切相关的草履虫K+通道基因（PAK）序列，利用以前报道的片段。从最近用于试验基因组测序项目的索引库中检索到另外8个独特的K+通道序列。这些蛋白质翻译的比对表明，虽然这15个基因在不同的时间有分歧，他们都保持了许多特征，只是一个亚类的后生动物K+通道（CNG/ERG型）。我们的研究结果表明，大多数基因的表达，因为所有预测的移码和同源比对中的几个差距包含草履虫内含子序列从逆转录PCR产物删除。15个基因组核苷酸序列中的一些变异涉及内含子的缺失，甚至在非常密切相关的序列之间，这表明过去可能发生逆转录。从现有的基因组序列外推表明草履虫携带多达几百个这种类型的K+通道基因。这一数量远远多于任何后生动物中已知的所有类型的K+通道基因的数量（例如，类似于人类中的80，类似于苍蝇中的30，和类似于拟南芥中的15）。为了理解这种多样性，我们讨论了几个可能的原因，他们的维护，包括响应于淡水环境中的变化，如草履虫与其他主要质膜蛋白的表达水平的变化。
K+-selective ion channels (K+ channels) have been found in bacteria, archaea, eucarya, and viruses. In Paramecium and other ciliates, K+ currents play an essential role in cilia-based motility. We have retrieved and sequenced seven closely related Paramecium K+-channel gene (PAK) sequences by using previously reported fragments. An additional eight unique K+-channel sequences were retrieved from an indexed library recently used in a pilot genome sequencing project. Alignments of these protein translations indicate that while these 15 genes have diverged at different times, they all maintain many characteristics associated with just one subclass of metazoan K+ channels (CNG/ERG type). Our results indicate that most of the genes are expressed, because all predicted frameshifts and several gaps in the homolog alignments contain Paramecium intron sequences deleted from reverse transcription-PCR products. Some of the variations in the 15 genomic nucleotide sequences involve an absence of introns, even between very closely related sequences, suggesting a potential occurrence of reverse transcription in the past. Extrapolation from the available genome sequence indicates that Paramecium harbors as many as several hundred of this one type of K+-channel gene. This quantity is far more numerous than those of K+-channel genes of all types known in any metazoan (e.g., similar to80 in humans, similar to30 in flies, and similar to15 in Arabidopsis). In an effort to understand this plurality, we discuss several possible reasons for their maintenance, including variations in expression levels in response to changes in the freshwater environment, like that seen with other major plasma membrane proteins in Paramecium.