Structure of the rainbow trout metallothionein B gene and characterization of its metal-responsive region.
The trout metallothionein (MT) genes consist of two members. We describe the structure of the first fish MT (tMT-B) gene which shows an overall resemblance but some remarkable differences with mammalian MT genes. The similarities included (i) tripartite structure of the gene, (ii) conservation of cysteine residues, and (iii) a TATAAA signal and two copies of metal-responsive elements (MREs). The differences consisted of (i) an AT-rich tMT-B promoter compared with highly GC-rich mammalian MT promoters and (ii) a lack of SP1-binding sites in the tMT-B promoter. Functional analysis of the tMT-B 5'-flanking region following fusion with the bacterial chloramphenicol acetyltransferase gene and its transfection into the rainbow trout hepatoma cell line revealed that sequences from positions -600 to +8 are sufficient for regulation by metals. Further deletion analyses of this fragment suggested that a minimum of 100 nucleotides upstream of the transcription initiation site are required for induction by cadmium and zinc. The tMT-B promoter was also functional in the human hepatoblastoma cell line, suggesting that an MT regulatory factor(s) is conserved in phylogenetically distant species like humans and fish.
Zafarullah
M
M
Department of Biological Sciences, University of Calgary, Alberta, Canada.
Bonham
K
K
Gedamu
L
L
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008668:Metallothionein / Q000235:genetics*; D008670:Metals / Q000494:pharmacology; D008969:Molecular Sequence Data; D005810:Multigene Family; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012487:Salmonidae / Q000235:genetics*; D014337:Trout / Q000235:genetics*
D008670:Metals; D008668:Metallothionein