Girgis S, Nasrallah I M, Suh J R, Oppenheim E, Zanetti K A, Mastri M G, Stover P J
Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853, USA.
Gene. 1998 Apr 14;210(2):315-24. doi: 10.1016/s0378-1119(98)00085-7.
The human cytoplasmic serine hydroxymethyltransferase (CSHMT) gene was isolated, sequenced and its expression characterized in human MCF-7 mammary carcinoma and SH_5Y5Y neuroblastoma cells. The 23-kb gene contains 12 introns and 13 exons; all splice junctions conform to the gt/ag rule. The open reading frame is interrupted by 10 introns, two of which are positionally conserved within the human mitochondrial SHMT gene. The gene is expressed with 330 nucleotides of 5' untranslated message within three exons. The 5' promoter region does not contain a consensus TATA, and primer extension and 5'-RACE studies suggest that transcription initiation occurs at multiple sites. Consensus motifs for several regulatory proteins, including SP1, mammary and neuronal-specific elements, NF1, a Y-box, and two steroid hormone response elements, are present within the first 408 nucleotides of the 5' promoter region. The human gene is expressed as multiple splice variants in both the 5' untranslated region and within the open reading frame, all due to exon excision. The splicing pattern is cell-specific. At least six CSHMT mRNA splice forms are present in MCF-7 cells; the gene is expressed as a full-length message as well as splice forms that lack exon(s) 2, 9 and 10. In 5Y cells, the predominant form of the message lacks exon 2, which encodes part of the 5' untranslated region, but does not contain deletions within the open reading frame. Western analysis suggests that the CSHMT gene is expressed as a single full-length protein in 5Y cells, but as multiple forms in MCF-7 cells. Multiple tissue Northern blots suggest that the CSHMT message levels and alternative splicing patterns display tissue-specific variations.
人类细胞质丝氨酸羟甲基转移酶（CSHMT）基因被分离、测序，并对其在人MCF-7乳腺癌细胞和SH_5Y5Y神经母细胞瘤细胞中的表达特性进行了研究。该23kb的基因包含12个内含子和13个外显子；所有剪接位点均符合gt/ag规则。开放阅读框被10个内含子打断，其中两个在内含子在人线粒体SHMT基因中的位置是保守的。该基因在三个外显子中表达，带有330个核苷酸的5'非翻译区。5'启动子区域不包含共有TATA盒，引物延伸和5'-RACE研究表明转录起始于多个位点。在5'启动子区域的前408个核苷酸内存在几种调节蛋白的共有基序，包括SP1、乳腺和神经元特异性元件、NF1、一个Y盒以及两个类固醇激素反应元件。该人类基因在5'非翻译区和开放阅读框内均表达为多种剪接变体，均是由于外显子切除所致。剪接模式具有细胞特异性。MCF-7细胞中至少存在六种CSHMT mRNA剪接形式；该基因表达为全长信息以及缺少外显子2、9和10的剪接形式。在5Y细胞中，主要的信息形式缺少外显子2，外显子2编码5'非翻译区的一部分，但开放阅读框内没有缺失。蛋白质免疫印迹分析表明，CSHMT基因在5Y细胞中表达为单一的全长蛋白，但在MCF-7细胞中表达为多种形式。多种组织的Northern杂交分析表明，CSHMT信息水平和可变剪接模式表现出组织特异性差异。
