一个含有25bp内含子的阴道毛滴虫Rabl-like新基因

目的 克隆和鉴定一个新的阴道毛滴虫Rabl-like基因（TvRabl-like）及其内含子。方法 我们从一阴道毛滴虫cDNA表达文库中分离出一个cDNA克隆，它与各物种的Rab家族蛋白有较高的同源性，因此我们进一步用BLASTP、RPS-BLAST、ClustalW和MEGA3等分析软件对该cDNA克隆进行了序列分析和进化树分析；用PCR和RT-PCR等技术分别对该基因组和mRNA进行了扩增和测序分析。结果 序列分析结果表明该eDNA克隆长705bp，开放阅读框具603bp，推测肽链含有200个氨基酸。序列比较分析结果提示该cDNA克隆所推测的蛋白质是一个Rabl亚家族的亚型。进化树分析也表明它属于阴道毛滴虫Rabl亚家族。基因组PCR扩增和测序分析表明该基因包含一个25bp的内含子，该内含子具有阴道毛滴虫和其它真核生物较大内含子所具备的典型的5’GT-AG-3’和分支位点基序。RT-PCR产物及其测序分析表明在该基因的转录本中存在着未剪切和剪切后的mRNA，说明确实有内含子的存在。结论 TvRabl-like基因属于阴道毛滴虫Rabl亚家族，该基因含有一个25bp的内含子。该内含子是至今发现的最小的阴道毛滴虫基因内含子之一，很可能也是真核生物中最小的内含子。对诸类最低等真核生物内含子的研究将有助于我们理解真核生物内含子的起源和进化。

A Novel Rabl-like Gene with A 25 bp Intron in Trichomonas vaginalis

Objective The aim of this study is to clone and characterize a novel Trichornonas vaginalis Rabllike gene （TvRabl-like） with a small intron. Methods The cDNA clone of TvRabl-like gene was isolated from a cDNA expression library and sequenced. Sequence analysis was performed using BLASTP, RPS-BLAST ClustalW programs. Phylogenetic analysis was carried out by MEGA3 program. The genomic DNA and mRNA of TvRabl-like gene were amplified using PCR and RT-PCR techniques respectively and also sequenced. Results The eDNA sequence of TvRabl-like gene had a length of 705 base pairs with an open reading frame of 603 bp. The deduced amino acid sequence from the open reading frame possessed 200 residuals corresponding to a putative M.W. 22532.2 and an estimated pI of 7.4. Sequence analysis demonstrated that TvRabl-like gene showed the highest homology to T. vaginalis Rabla （63% identity and 79% similarity） and the Rabl subfamily of other species, suggesting that the deduced amino acid sequence from this eDNA clone was a Rabl isoform. Phylogenetic analysis showed that TvRabl-like gene was clustered with T.vaginalis Rabl subfamily in the phylogenetic tree. Sequencing of the PCR product of genomic DNA revealed that the genomic DNA possessed a 25 bp intron which contained canonical 5＇GT-AG-3＇ and branch site motifs as those larger introns found in T.vaginalis and other eukaryotes. The analysis of RT-PCR products demonstrated the presence of the unspliced mRNA and spliced mRNA, indicating that there was a intron. Conclusion These data suggest that TvRabl-like gene belongs to T.vaginalis Rabl subfamily. TvRabl-like gene possesses a 25 bp spliceosomal intron which is the smallest one of the introns identified in this deepest-branching protist and might be the shortest intron of eukaryotes. Study of those introns might provide more insights into the intron evolution of eukaryotes.