Cadmium restores in vitro splicing activity inhibited by zinc-depletion

Zinc (Zn)-depletion inhibits the second step of RNA splicing, namely exon-ligation. To investigate the effects of cadmium (Cd) and other metal ions on RNA splicing inhibited by Zn-depletion, we measured in vitro splicing activities in the presence of these metals. Zn-depletion in the splicing reaction mixture was achieved by addition of a Zn-chelator, 1,10-phenanthroline. Cd(II) at 1, 5 and 10 microM restored the splicing activity to 2, 24 and 72% of that in the control reaction mixture, while higher concentrations of Cd(II) decreased the splicing activity, and more than 50 microM Cd(II) showed a complete absence of spliced products. Hg(II) also restored the splicing activity, albeit to a lesser extent, since 5 and 10 microM Hg(II) restored the splicing activity to 3 and 4% of the control value. The other metal ions examined in this study, Co(II), Cu(II), Mg(II) and Mn(II), did not show any restoration of the splicing activity. We concluded that Cd(II) could restore the in vitro splicing activity inhibited by Zn-depletion, although higher concentrations of Cd(II) prevented progress of the RNA splicing reaction. These results suggest that Cd(II) has a bifunctional property regarding RNA splicing, and is stimulatory at low concentrations and inhibitory at high concentrations.