FIG. 1.

(A) The level of c-Myc RNA decreases following the induction of C/EBPα gene expression. U937 stable cell lines that contain either a rat C/EBPα cDNA under the control of the human metallothionein promoter (U937α#2) or the empty metallothionein expression vector alone were harvested for total RNA at the indicated time points following the addition of ZnSO₄ to the culture medium. (Top) Northern hybridization with a c-Myc cDNA probe. (Middle) Northern hybridization with a C/EBPα cDNA probe. (Bottom) The Northern blot was stripped and rehybridized with a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) cDNA probe to control for RNA loading and integrity. (B) The expression of c-Myc protein decreases as the level of C/EBPα protein increases. The U937α#2 stable line was harvested for cell lysates for Western analysis at the indicated time points following incubation with ZnSO₄. (Top) Western blot hybridized with c-Myc antiserum. (Middle) The same Western blot hybridized with C/EBPα antiserum. (Bottom) The same Western blot hybridized with β-tubulin antibody to control for protein loading and integrity.