The synthesis of Galalpha1-3Gal-terminated oligosaccharides (alpha-Gal) epitopes has been interrupted during the course of evolution, starting with Old World primates. Partial sequences similar to the alpha1,3-galactosyltransferase (alpha1,3GalT) gene, which governs the synthesis of alpha-Gal epitopes, have been detected in the human genome and were found to correspond to pseudogenes. We completed the sequence of the human alpha1,3GalT pseudogene present on chromosome 9 and found it to be organized like the murine alpha1,3GalT gene. In human cell lines and several normal and tumor tissues we detected truncated transcripts corresponding to this pseudogene. Considering these mRNAs, translation of an open reading frame containing the first four translated exons but missing the two catalytic exons could predict a truncated alpha1,3GalT polypeptide that should be enzymatically inactive. We show that transcription of human alpha1,3GalT is prematurely terminated at the level of a strong transcriptional stop signal in the middle of intron VII. We were able to reproduce this effect in vitro by subcloning the implicated DNA region upstream from a reporter cDNA. The premature transcriptional arrest of human alpha1,3-GalT gene leads to an ectopic splicing event and to the connection of a short intronic sequence downstream from translated exons. Finally, we show that these truncated transcripts are overexpressed in cell lines with modifications of O-glycans.

中文翻译：

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完整的α1，3-半乳糖基转移酶基因存在于人类基因组中并被部分转录。

从旧大陆灵长类动物开始，在进化过程中中断了Galalpha1-3Gal末端寡糖（alpha-Gal）表位的合成。在人类基因组中已检测到与控制α-Gal表位合成的alpha1,3-半乳糖基转移酶（alpha1,3GalT）基因相似的部分序列，并发现其与假基因相对应。我们完成了存在于9号染色体上的人alpha1,3GalT假基因的序列，发现它的结构像鼠的alpha1,3GalT基因一样。在人类细胞系以及一些正常和肿瘤组织中，我们检测到了与该假基因相对应的截短的转录本。考虑到这些mRNA，如果一个开放阅读框的翻译包含前四个翻译的外显子，但缺少两个催化外显子，则可以预测a1被截断，应该是无酶活性的3GalT多肽。我们表明，人类α1、3GalT的转录在内含子VII中间强转录终止信号的水平过早终止。我们能够通过在报告子cDNA上游上游亚克隆涉及的DNA区来在体外重现这种效应。人类alpha1,3-GalT基因的过早转录停滞导致异位剪接事件，并导致短的内含子序列连接到翻译的外显子的下游。最后，我们显示这些截短的转录本在O-聚糖修饰的细胞系中过表达。我们能够通过在报告子cDNA上游上游亚克隆涉及的DNA区来在体外重现这种效应。人类alpha1,3-GalT基因的过早转录停滞导致异位剪接事件，并导致短的内含子序列连接到翻译的外显子的下游。最后，我们显示这些截短的转录本在O-聚糖修饰的细胞系中过表达。我们能够通过在报告子cDNA上游上游亚克隆涉及的DNA区来在体外重现这种效应。人类alpha1,3-GalT基因的过早转录停滞导致异位剪接事件，并导致翻译的外显子下游的短内含子序列的连接。最后，我们显示这些截短的转录本在O-聚糖修饰的细胞系中过表达。