Metal-induced expressing of mammal Metallothionein-1 gene in cyanobacteriato promote cadmium-binding preferences

The metal(zinc)-inducible smtA gene promoter (smt O-P) from cyanobacteria w as applied for the expression of mouse MT-1 cDNA in the filamentous cyanoba cterium Anabaena sp. PCC 7120 to enhance its metal-binding capability and t o change its main binding specificity from zinc to cadmium. Shuttle express ion vector pKT-MRE transformed the cyanobacterial cells by triparent conjug al transfer. Positive clones were screened and identified by streptomycin, DNA dot blot, SDS-PAGE and Western blot analysis. Photosynthetic oxygen evo lution and metal atom absorption indicated that under the cadmium stress th e metal-induced expression of foreign mMT-1 doubled their cadmium resistanc e and developed cells showing a much higher preference to absorb cadmium ot her than zinc in medium. The cadmium content in cell extract rose from 11% to 36%, and the cadmium cleared from media by transgenic cells rose from 18 % to 62%. There was only a slight enhancement for zinc binding in the wild or transgenic type.