The human nramp2 gene: Characterization of the gene structure, alternative splicing, promoter region and polymorphisms
The human nramp2 gene: Characterization of the gene structure, alternative splicing, promoter region and polymorphisms
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DOI：
10.1006/bcmd.1998.0186
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发表时间：
1998-05-15
影响因子：
2.3
通讯作者：
Beutler, E
中科院分区：
文献类型：
--
作者：
Lee, PL;Gelbart, T;Beutler, E
Nramp2是编码跨膜蛋白的基因，所述跨膜蛋白在金属（特别是铁）转运中是重要的。nramp2的突变已被证明是与小红细胞性贫血的小鼠和贝尔格莱德大鼠的铁转运缺陷。Nramp2在3 '非翻译区含有经典的铁响应元件，其赋予铁依赖性mRNA稳定性。在这份报告中，我们描述了一个剪接变异形式的人nramp2的羧基末端18个氨基酸取代25个新的氨基酸，并有一个新的3 '非翻译区缺乏一个经典的铁响应元件。nramp2基因的剪接形式nramp2 non-IRE是由一个额外的外显子剪接到末端编码外显子上而形成的，nramp2基因由17个外显子组成，长度超过36 kb。与同源基因nramp1相比，它含有额外的5 '外显子和内含子（外显子和内含子1）以及额外的3'外显子（外显子17）和内含子（内含子16）。额外的外显子和内含子是nramp2（> 36 kb）和nramp1（12 kb）之间长度差异的主要原因。nramp2外显子3 - 15的外显子-内含子边界与nramp1外显子2 - 14同源。nramp2 5 '调控区含有两个CCAAT盒，但缺少TATA盒。nramp2基因的5 ′调控区还含有5个潜在的金属反应元件（MRE）、3个潜在的SP1结合位点和1个γ-干扰素调控元件，这些MRE与金属硫蛋白-Ⅱ基因中的MRE相似。其中之一，1303C--> A，发生在nramp2的编码区，导致氨基酸从亮氨酸变为异亮氨酸。一个多态性，1254 T/C，也发生在nramp2的编码区，但不会导致氨基酸的变化。其他3个多态性位于内含子内（IVS2 + 11A/G、IVS4 + 44C/A和IVS6 + 538G/Gdel）。此外，在内含子3中还发现了一个多态性微卫星TATATCTATATATC（TA）（6 - 7）（CA）（10 - 11）CCCCCTATA（TATC）（3）（TCTG）（5）（TCCG（TCTA）（6）。这些外显子中的任一个的缺失将导致保留在框内的序列，但将产生分别缺乏跨膜区7或8的蛋白质。单个跨膜结构域的缺失将产生严重的拓扑后果。对血色病患者的nramp 2基因编码区进行了检查，发现血色病基因HFE有或没有突变，结果正常。1例血色素沉着症患者，HFE基因型正常，1303C-> A突变为杂合子。此外，在一项血色素沉着症患者突变HFE和正常HFE基因的检查中，我们没有观察到任何一组与特定nramp2单倍型的连锁不平衡。这些数据表明nramp2突变通常与血色病无关。(C)北京：科学出版社.
Nramp2 is a gene encoding a transmembrane protein that is important in metal transport, in particular iron. Mutations in nramp2 have been shown to be associated with microcytic anemia in mk/mk mice and defective iron transport in Belgrade rats. Nramp2 contains a classical iron responsive element in the 3' untranslated region that confers iron dependent mRNA stabilization. In this report, we describe a splice variant form of human nramp2 that has the carboxyl terminal 18 amino acids substituted with 25 novel amino acids and has a new 3' untranslated region lacking a classical iron-responsive element. This splice form of nramp2, nramp2 non-IRE, was found to be derived from splicing of an additional exon into the terminal coding exon.The nramp2 gene is comprised of 17 exons and spans more than 36 kb. It contains an additional 5' exon and intron (exon and intron 1) and an additional 3' exon (exon 17) and intron (intron 16) as compared to nramp1, a homologous gene. The additional exons and introns account for much of the difference in length between nramp2 (>36 kb) and nramp1 (12 kb). The exon-intron borders of nramp2 exons 3-15 are homologous to nramp1 exons 2-14. The nramp2 5' regulatory region contains two CCAAT boxes but lacks a TATA box. The 5' regulatory region of nramp2 also contains five potential metal response elements (MRE's) that are similar to the MRE's found in the metallothionein-II, gene, three potential SP1 binding sites and a single gamma-interferon regulatory element.Five single nucleotide mutations or polymorphisms were identified within the nramp2 gene. One of these, 1303C-->A, occurs in the coding region of nramp2 and results in an amino acid change from leucine to isolecine. A polymorphism, 1254T/C, also occurs in the coding region of nramp2 but does not cause an amino acid change. The other 3 polymorphisms are within introns (IVS2+11A/G, IVS4+44C/A, and IVS6+538G/Gdel). In addition, a polymorphic microsatellite TATATCTATATATC(TA)(6-7)(CA)(10-11)CCCCCTATA(TATC)(3)(TCTG)(5)(TCCG(TCTA)(6) was identified in intron 3.Analysis of cDNA derived by direct amplification of reversed transcribed RNA or cDNA clones isolated from a library provide evidence of skipping of exons 10 and 12 of nramp2. Deletion of either of these exons would result in a sequence that remains in frame yet would generate a protein that would lack transmembrane spanning region 7 or 8 respectively. The deletion of a single transmembrane domain would have severe topological consequences.The coding region of the nramp2 gene of hemochromatosis patients with or without mutations in the hemochromatosis gene, HFE, were examined and found to be normal. One hemochromatosis patient, with a normal HFE genotype, was heterozygous for the 1303C-->A mutation. Furthermore, in an examination of hemochromatosis patients with mutant HFE and normal HFE genes, we did not observe a linkage disequilibrium of either group with a particular nramp2 haplotype. These data suggest that mutations in nramp2 are not commonly associated with hemochromatosis. (C) 1998 Academic Press.