Induction with CuSO4 - Concentration? (Mar/14/2005 )

Hi everyone,
I'm trying to express a protein from a metallothionein promoter and plan to induce this expression with copper sulphate. Could anyone suggest what sort of concentration i should use to induce expression without harming my cells (Drosophila S2's). Will the amount inducer determine the level of expression or does it work on the all or nothing principle - the promoter has several regulatory regions so i'm assuming that the higher the [CuSO4], the more regulatory regions will be occupied and the greater the level of expression. Plz help, thanks.

I always use 200µM CuSO4 with DS-2 cells (plasmid is pMta)

mike