Structure and metal-regulated expression of the gene encoding Xenopus laevis metallothionein-A.
To investigate the regulation of amphibian metallothionein(MT)-encoding genes, we have isolated and sequenced the XlMT-A gene encoding Xenopus laevis (Xl) MT-A. The gene displays an overall structure similar to that of mammalian MT, with three exons interrupted by two introns. The promoter region contains a typical TATA box and two metal regulatory elements (MRE) within the first 100 bp upstream from the transcription start point (tsp). The transition metal ion (Mc2+) inducibility of the promoter was studied by transient expression experiments in CV-1 African green monkey kidney cells, using different DNA fragments from the 5'-flanking region of XlMT-A fused to the bacterial cat reporter gene. The first 145 bp upstream from the tsp are sufficient to confer inducibility of cat by Cd2+. Constructs bearing only the most proximal MRE are not inducible by Me2+, thus suggesting that both MRE are required for Me2+ induction. Recognition sites for the transcription factors, AP-1 and AP-2, are located within the first 180 bp of the promoter region and these elements appear to be involved in controlling the constitutive basal level of expression of this MT.
Saint-Jacques
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Centre de recherche en cancérologie de l'Université, L'Hôtel-Dieu de Québec, Canada.
April
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Séguin
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002413:Cations, Divalent / Q000494:pharmacology*; D002461:Cell Line, Transformed; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D005091:Exons; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D005796:Genes; D007438:Introns; D008322:Mammals / Q000235:genetics; D008668:Metallothionein / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D016415:Sequence Alignment; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid; D016385:TATA Box; D014157:Transcription Factors / Q000378:metabolism; D014337:Trout / Q000235:genetics; D014982:Xenopus laevis / Q000235:genetics* / Q000378:metabolism
D002413:Cations, Divalent; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D008668:Metallothionein