Rodriguez I R, Mazuruk K, Schoen T J, Chader G J
Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1994 Dec 16;269(50):31969-77.
Hydroxyindole-O-methyltransferase (HIOMT) catalyzes the last step in the metabolic pathway that synthesizes the hormone melatonin. We have found HIOMT mRNA present in small amounts in human retina and in relatively high abundance in the pineal gland. Two distinct 5' ends were found in human retina using a solid-phase 5'-rapid amplification of cDNA ends technique. The two 5' regions appear to originate from two distinct putative promoters. Although many similarities exist between the two promoters, they contain distinctive elements. Putative promoter A, for example, contains a recently discovered photoreceptor-conserved element (PCE-1, CAATTAAG) at -27 not found in promoter B, while promoter B contains an Ap1 site (ATGAGTCAA) at -166 and an octamer site (ATGCAAT) at -59 not found in promoter A. The HIOMT messages are also alternatively spliced in between exons 6 and 8, generating three distinct messages. One of the alternatively spliced messages contains a line-1 repetitive element that is spliced into the mRNA precisely as exon 6. Importantly, the downstream open reading frame is not altered by any of these splicing combinations. The gene is approximately 35 kilobases long containing either 9 or 10 exons (including the line-1 element) depending on which promoter is active. All of the splice sites follow the GT/AG rule. The dual promoters and opportunities for alternative splicing suggest a variety of mechanisms for control of HIOMT expression and biological activity in different tissues not previously recognized.
羟基吲哚 - O - 甲基转移酶（HIOMT）催化合成褪黑素的代谢途径中的最后一步。我们发现HIOMT mRNA在人类视网膜中少量存在，而在松果体中含量相对较高。使用固相5' - cDNA末端快速扩增技术在人类视网膜中发现了两个不同的5'端。这两个5'区域似乎源自两个不同的假定启动子。尽管两个启动子之间存在许多相似之处，但它们包含独特的元件。例如，假定启动子A在 - 27处含有一个最近发现的光感受器保守元件（PCE - 1，CAATTAAG），而在启动子B中未发现；启动子B在 - 166处含有一个Ap1位点（ATGAGTCAA），在 - 59处含有一个八聚体位点（ATGCAAT），而在启动子A中未发现。HIOMT的信使核糖核酸（mRNA）在第6和第8外显子之间也存在可变剪接，产生三种不同的信使核糖核酸。其中一种可变剪接的信使核糖核酸包含一个LINE - 1重复元件，它精确地作为第6外显子剪接到mRNA中。重要的是，下游开放阅读框不会因任何这些剪接组合而改变。该基因大约35千碱基长，根据哪个启动子活跃，包含9个或10个外显子（包括LINE - 1元件）。所有的剪接位点都遵循GT/AG规则。双重启动子和可变剪接的机会表明存在多种机制来控制HIOMT在不同组织中的表达和生物学活性，这是以前未被认识到的。
