Zip4 RNAi and control RNAi Hepa cells, purified by flow sorting, were seeded at low density to facilitate a rapid onset of zinc deficiency, blocked using hydroxyurea to increase the number of cells in G0/G1, and then released from the block to reinitiate the cell cycle in zinc-deficient medium (Fig. 4). The gene discussed is SLC39A4; the disease is Zinc deficiency.