Figure 3.

Titration of zinc shows parallel effects on level of expression and silencing within clones. (A) Clones 10 and 12 were induced for 24 h with increasing concentrations of zinc sulfate up to 80 μM. β-gal activity in each of the aliquots was then assayed by MUG conversion as in Fig. 2. (B) Clones 10 and 12 were removed from G418 selection and maintained in medium containing varying concentrations of zinc sulfate, up to 80 μM, as in A. FACS-gal was performed at weekly intervals; the histograms shown are derived from the 2-wk time point. Concentration of zinc is shown at the right. The percentage figures within the histogram boxes represent the proportion of cells in the positive peak. The effect of zinc on silencing parallels the effect on expression level in both clones.