Cloning of crucian carp (Carassius cuvieri) metallothionein-II gene and characterization of its gene promoter region

The genomic DNA of crucian carp (Carassius cuvieri) metallothionein-II (ccMT-II), with its upstream region, was obtained. The sequence analysis of its upstream region revealed several putative cis-acting elements including seven metal regulatory elements (MREs), three activator protein 1 (AP1), two glucocorticoid response elements (GREs), etc. The seven MREs locate into two clusters, a distal cluster with four MREs within −800/−600 bp from the translation start site and a proximal cluster with three MREs close to TATA box. In transient luciferase gene expression assays, both of the distal and proximal cluster MREs have significantly shown synergistic effects in the transcription of ccMT-II gene; the proximal cluster of MREs serves as the major elements in metal inducing activity; Zn2+ and Cd2+ served as much stronger inducers than Cu2+ shown in ccMT-II expression. The two GRE homologous sequences in ccMT-II promoter showed not to be inductive in either HepG2 or HEK293.