Deen P M, Terwel D, Bussemakers M J, Roubos E W, Martens G J
Department of Animal Physiology, University of Nijmegen, The Netherlands.
Eur J Biochem. 1991 Oct 1;201(1):129-37. doi: 10.1111/j.1432-1033.1991.tb16265.x.
In the pars intermedia of the pituitary the prohormone proopiomelanocortin (POMC) is tissue-specifically processed to, among other peptides, alpha-melanotropin (alpha MSH). In the South African clawed toad Xenopus laevis this hormone mediates the process of background adaptation: release of alpha-MSH causes darkening of the animal, while inhibition of alpha-MSH release results in a pale toad. Elevated release of alpha-MSH coincides with a higher rate of POMC gene transcription. The present study aims to find possible transcriptional regulatory elements in the Xenopus POMC gene. For that purpose the complete nucleotide sequence of the POMC gene and its 5'- and 3'- flanking regions were determined and analyzed. The Xenopus POMC gene promoter contains several regions which may be regulatory DNA elements in view of their similarity with corresponding regions of mammalian POMC gene promoters. In the rat POMC gene promoter, many of these regions represent protein-binding sequences. Besides the promoter sequence and the protein-coding sequences, no other segments with significant identity between the Xenopus and human POMC genes were found. Intron A of the Xenopus POMC gene contains a simple sequence, (TATC)76, and a JH12 repetitive element, while the 3'-flanking region contains a repetitive-EcoRI-monomer-2 element. Comparison of the JH12 sequence of the POMC gene with JH12 sequences from other Xenopus genes revealed a 335-bp consensus sequence which is flanked by a 30-bp inverted repeat. This JH12 consensus sequence is significantly larger than the previously reported JH12 core region. Alignment of intron B of the Xenopus POMC gene with database sequences revealed a consensus sequence of a novel Xenopus repetitive element of 330 bp flanked by a nearly perfect inverted repeat, indicating that this element may be a transposon-like element.
在垂体的中间部，激素原阿黑皮素原（POMC）会进行组织特异性加工，生成多种肽类，其中包括α-促黑素（α-MSH）。在南非爪蟾非洲爪蟾中，这种激素介导背景适应过程：α-MSH的释放会使动物皮肤变黑，而抑制α-MSH的释放则会使蟾蜍皮肤变浅。α-MSH释放增加与POMC基因转录速率提高同时出现。本研究旨在寻找非洲爪蟾POMC基因中可能的转录调控元件。为此，测定并分析了POMC基因及其5'和3'侧翼区域的完整核苷酸序列。非洲爪蟾POMC基因启动子包含几个区域，鉴于它们与哺乳动物POMC基因启动子相应区域的相似性，这些区域可能是调控DNA元件。在大鼠POMC基因启动子中，许多这些区域代表蛋白质结合序列。除了启动子序列和蛋白质编码序列外，未发现非洲爪蟾和人类POMC基因之间有其他具有显著同源性的片段。非洲爪蟾POMC基因的内含子A包含一个简单序列（TATC）76和一个JH12重复元件，而3'侧翼区域包含一个重复-EcoRI-单体-2元件。将POMC基因的JH12序列与其他非洲爪蟾基因的JH12序列进行比较，发现一个335 bp的共有序列，其两侧是一个30 bp的反向重复序列。这个JH12共有序列明显大于先前报道的JH12核心区域。将非洲爪蟾POMC基因的内含子B与数据库序列进行比对，发现一个330 bp的非洲爪蟾新型重复元件的共有序列，其两侧是近乎完美的反向重复序列，表明该元件可能是一个转座子样元件。
