Growth kinetics of the parental MEL-B8/3 cells and transfectants of the mutant PU.1/Spi-1 genes under various culture conditions. Parental MEL-B8/3 cells (•), PU.1-Δ E-sense clone 1 cells (▪), PU.1-Δ E-antisense clone 1 cells (□), PU.1-Δ A-sense clone 1 cells (▴), and PU.1-Δ A-antisense clone 1 cells (▵) were cultured in the ordinary medium (A), in the medium containing 1.5% DMSO (B), in the medium containing 100 μmol/L ZnCl₂ (C), or in the medium containing 1.5% DMSO and 100 μmol/L ZnCl₂ (D). Cells (2 × 10⁶) were placed in 10 mL of the culture medium and the cell number was determined every 24 hours. Mean values and standard deviations of three independent experiments are shown.