Figure 3.

Translation of truncated C/EBPα and C/EBPβ proteins from downstream initiation sites depends on the uORF. Schematic representations of the mRNAs with potential initiation sites indicated in relation to the protein bands are shown at left. COS-1 cells were transiently transfected with C/EBP wild-type (wt) and mutant constructs and analyzed for C/EBP protein expression by immunoblotting. In ΔD mutants, the uORF translation initiation site is mutated to a noninitiation site. In the Aopt mutant, the sequence context of site A is mutated to an optimal Kozak sequence. The X mutants harbor an additional, optimal translation initiation site upstream of site C. (a) rC/EBPα; (b) cC/EBPα; (c) rC/EBPβ; (d) cC/EBPβ.