Metal interaction and regulation of Tetrahymena pigmentosa metallothionein genes

The patterns of expression of two metallothionein (MT) genes, MT-1 and MT-2, previously identified as Cd-MT and Cu-MT, were analysed in Tetrahymena pigmentosa in response to metal inducers cadmium, copper and zinc and to a mixture of copper and cadmium at appropriate concentrations. Co-treatment induces synergistic accumulation of both metals and higher expression of MT-mRNAs in the first few hours. mRNA levels were observed not to completely correlate with MT-protein levels, suggesting that post-transcriptional regulation may be involved in MT induction. MT-1 is induced to higher levels than MT-2. Zinc does not induce any MT expression. The lowest level of mRNA was observed for MT-2, induced only by copper. Cadmium is a powerful inducer of the MT-1 gene, although a very low transcription rate by copper occurs in the first hour.