Flow cytometry analysis of electroporated DF-1 cells. (a) The proportion of eGFP-expressing cells are indicated. Arrows denote cells of the non-expressing population. (b) The effect of cis-acting elements on the coefficient of variation (CV) in eGFP expression driven by CMV and CAG promoters. A significant model effect was found on CV among the eight constructs (P < 0.0001). Means with different letters (a, b, c, d, e, f, g) differ significantly (P < 0.05; F value = 2927.53; total degree of freedom = 23). Data represent the mean of three replicates, and error bars indicate ± S.D.(n = 3 in each plasmid).