Study on the structure of gene of histamine inactivating enzyme and its regulation of expression

1.人组胺N-甲基转移酶(HMT)的基因结构利用人组胺N-甲基转移酶(HMT)基因对人基因组文库(EMBL3)进行筛选，得到多个基因组克隆，并测定其结构。此外，我们还利用从人肾组织中提取的nRNA，通过引物延伸的方法分析了一个转录点。结果表明，扩增法检测到2条主要条带。根据HMT基因下游转录点的结构分析，人类HMT基因由6个外显子组成，第一个外显子含有137b编码区和相对较长的383b非编码区。在转录点上游的2kb区域没有TATA类序列，但检测到3SP-1，5-GATA，2个LRF-1，5 LBP-1结合序列。另一方面，由于另一个主要转录点位于另一个转录点的上游约100b，因此有可能出现新的第一外显子。正如在其他基因中所报道的那样，推测可能的…交替2.HMT基因的多态性，根据我们先前的报道和R Weishilboum的报道，编码区的核苷酸序列发生了两次变化。密码子105内的核苷酸314是T或C，导致密码子编码异亮氨酸或苏氨酸。密码子199内的595位核苷酸是A或G，产生的是异亮氨酸或缬氨酸。此外，我们还发现了在第一外显子第89位核苷酸中缺失8个核苷酸(CTAACAAA)的克隆。此外，第6外显子附近的CA重复序列是多态的，我们分析了100名正常个体的CA重复序列数目。结果表明，HMT基因的CA重复数分布在15~30之间，是HMT基因多态性的有用标志。3.HMT基因与哮喘的遗传连锁。哮喘的关键因素--气道高反应性被认为是遗传的生理特征之一。HMT活性水平与豚鼠对组胺的气道收缩反应密切相关。在这方面，为了研究HMT基因是否与哮喘有关，我们比较了哮喘患者和正常个体的多态性。结果表明，CA重复数的分布与正常人有显著差异。其中，CA重复数小于20似乎是哮喘的危险因素。较少

1.Gene structure of human histamine N-methyltransferase (HMT)We obtained several genomic clones by screening human genomic library (EMBL3) with human HMT cDNA and determined its structure. In addition, we analyzed a transcriptional point by a primer extension method with nRNA extracted from human kidney. As a result, the experiment of primer extension method revealed that 2 major bands was detected. According to an analysis of HMT gene structure based on the transcriptional point locating downstream, human HMT gene consists of 6 exons, and the first exon contains a 137b coding region and a realtively long 383b noncoding region. While TATA-like sequence did not exist in 2kb region upstream to a transcriptional point, 3SP-1,5 GATA,2 LRF-1,5 LBP-1binding sequence were detected. On the other hand, since another major transcriptional point located about 100b upstream to other one, it is possible to expect a new first exon. As reported in other genes, it was speculated that possible alternat … More ive transcriptional points were involved in a tissue-specific expression.2.Polymorphism of HMT geneTo date, sccording to our previous report and the report by R Weishilboum, two changes of nucleotide sequence in coding region. Nucleotide 314 within codon 105 is a T or a C,resulting in codons that encode isoleucine or threonine. Nucleotide 595 within codon 199 is an A or G,resulting isoleucine or valine. In addition, we found clones which lack of 8 nuleotides (CTAACAAA) in ncleotide 89 of first exon. Furthermore CA repeat sequense near 6th exon was polymorphic and we analyzed the number of CA repeat among 100 normal individuals. As a result, CA repeat number distributed from 15 to 30 and was thought to be a useful marker of polymorphism of HMT gene.3.Genetic linckage of HMT gene to bronchial asthmaThe airway hyperresponsiveness, a critical factor of bronchial asthma, has been recognized as one of physical characteristics inherited genetically. The level of HMT activity is closely associated with airway contractile response to histamine in guinea pigs. In this regard, to examine whether HMT gene is linked to bronchial asthma, we compared polymorphism of asthmatics to that of normal individuals. As a result, the distribution of CA repeat number was significantly different from that of normal individuals. Especially, CA repeat size smaller than 20 seemed to be a risk factor for bronchial asthma. Less