Brünen-Nieweler C, Schmidt H J, Heckmann K
Institute of General Zoology and Genetics, University of Münster, F.R.G.
Gene. 1991 Dec 30;109(2):233-7. doi: 10.1016/0378-1119(91)90613-g.
The portion of the pheromone 3 (Phr3)-encoding gene (phr3) of Euplotes octocarinatus, corresponding to secreted Phr3 was isolated using the polymerase chain reaction and oligodeoxyribonucleotide primers flanking the Phr3-encoding cDNA. Unexpectedly, the sequence analysis revealed that this gene is interrupted by two introns with lengths of 63 bp and 72 bp. These introns belong to the class of nuclear pre-mRNA introns and contain typical 5'- and 3'-consensus sequences, as well as unique features. Our findings constitute the first example of introns in any Euplotes species and the first case of multiple introns in hypotrichous ciliates. In ciliates such as Euplotes, the macronucleus is the transcriptionally active nucleus. It develops from a micronucleus in a process which involves chromosome breakage and the elimination of up to 95% of the micronuclear genome. The existence of the introns in the macronuclear version of phr3 shows that, in spite of this extensive elimination, some noncoding sequences are nevertheless retained in the macronucleus of hypotrichous ciliates. It was recently discovered by Meyer et al. [Proc. Natl. Acad. Sci. USA 88 (1991) 3758-3761] that the Phr3-encoding cDNA contains three in frame TGA triplets coding for cysteine. The genomic sequence of phr3 confirms this finding.
利用聚合酶链反应和位于编码Phr3的cDNA两侧的寡脱氧核糖核苷酸引物，分离出了八肋游仆虫信息素3（Phr3）编码基因（phr3）中与分泌型Phr3相对应的部分。出乎意料的是，序列分析显示该基因被两个长度分别为63 bp和72 bp的内含子打断。这些内含子属于核前体mRNA内含子类别，包含典型的5'和3'共有序列以及独特特征。我们的发现构成了游仆虫属物种中内含子的首个实例，也是腹毛目纤毛虫中存在多个内含子的首个案例。在诸如游仆虫这样的纤毛虫中，大核是转录活跃的细胞核。它由小核发育而来，这个过程涉及染色体断裂以及高达95%的小核基因组的消除。phr3大核版本中内含子的存在表明，尽管有这种广泛的消除，一些非编码序列仍保留在腹毛目纤毛虫的大核中。迈耶等人[《美国国家科学院院刊》88（1991）3758 - 3761]最近发现，编码Phr3的cDNA包含三个编码半胱氨酸的框内TGA三联体。phr3的基因组序列证实了这一发现。
