IDENTIFICATION OF A NOVEL FIRST EXON IN THE HUMAN DYSTROPHIN GENE AND OF A NEW PROMOTER LOCATED MORE THAN 500-KB UPSTREAM OF THE NEAREST KNOWN PROMOTER
IDENTIFICATION OF A NOVEL FIRST EXON IN THE HUMAN DYSTROPHIN GENE AND OF A NEW PROMOTER LOCATED MORE THAN 500-KB UPSTREAM OF THE NEAREST KNOWN PROMOTER
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DOI：
10.1172/jci117417
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发表时间：
1994-09-01
影响因子：
15.9
通讯作者：
MATSUO, M
中科院分区：
文献类型：
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作者：
NISHIO, H;TAKESHIMA, Y;MATSUO, M
在杜氏和贝克肌营养不良症患者中发生突变的肌营养不良蛋白基因是已知的最大的人类基因。到目前为止，已经确定了五种替代启动子。在这里，我们表明，一种新的肌营养不良蛋白亚型与不同的第一外显子可以通过转录起始在以前未确定的替代启动子。该病例研究是杜氏肌营养不良症的患者，其具有从肌营养不良蛋白基因的5'末端延伸至外显子2的缺失，包括先前在基因的5'部分中定位的所有启动子。发现来自淋巴母细胞的转录物含有对应于外显子3的序列，表明该外显子上游存在新的启动子。扩增的cDNA对应于新转录本的5'端的核苷酸序列表明，外显子3的5'端由9个密码子延伸，其中只有最后一个（大部分3 '）编码甲硫氨酸。从新的外显子上游的基因组核苷酸序列，如使用反向聚合酶链反应测定，揭示了类似于TATA盒，八聚体基序和MEF-2元件的序列的存在。所鉴定的启动子/外显子没有定位到内含子2，如可能已经预期的，而是定位到先前鉴定的启动子的最5'上游500 kb以上的位置，从而向肌营养不良蛋白基因添加500 kb。新的启动子区的部分序列与某些中等重复频率的重复序列非常相似。这些发现可能有助于我们了解抗肌萎缩蛋白基因的分子进化。
The dystrophin gene, which is mutated in patients with Duchenne and Becker muscular dystrophies, is the largest known human gene. Five alternative promoters have been characterized until now. Here we show that a novel dystrophin isoform with a different first exon can be produced through transcription initiation at a previously unidentified alternative promoter. The case study presented is that of a patient with Duchenne muscular dystrophy who had a deletion extending from the 5' end of the dystrophin gene to exon 2, including all promoters previously mapped in the 5' part of the gene. Transcripts from lymphoblastoid cells were found to contain sequences corresponding to exon 3, indicating the presence of new promoter upstream of this exon. The nucleotide sequence of amplified cDNA corresponding to the 5' end of the new transcript indicated that the 5' end of exon 3 was extended by 9 codons, only the last (most 3') of which codes for methionine. The genomic nucleotide sequence upstream from the new exon, as determined using inverse polymerase chain reaction, revealed the presence of sequences similar to a TATA box, an octamer motif and an MEF-2 element. The identified promoter/exon did not map to intron 2, as might have been expected, but to a position more than 500 kb upstream of the most 5' of the previously identified promoters, thereby adding 500 kb to the dystrophin gene. The sequence of part of the new promoter region is very similar to that of certain medium reiteration frequency repetitive sequences. These findings may help us understand the molecular evolution of the dystrophin gene.