Mut10 C/EBPα expresses enhanced levels of a 30-kDa protein. (A) Schematic depiction of the vectors used for these studies. The cDNA for mut10 C/EBPα was inserted into the FMEV-GFP retroviral vector. Cotranslation of eGFP is mediated by an internal ribosomal entry site (I). A posttranscriptional regulatory element (PRE) from the woodchuck hepatitis virus increases expression levels. (B) Schematic representation of predicted proteins expressed by wild-type or mut10 C/EBPα cDNAs. Due to a 7-bp deletion resulting in a frameshift at amino acid 39 and a termination codon at amino acid 159, the full-length 42-kDa protein is truncated and enhanced expression of a 30-kDa protein is observed. (C) Coexpression of eGFP in the vectors allows the detection of both transduced and nontransduced cells. The eGFP fluorescence was measured by flow cytometry in BM cells infected with either the control “empty” vector (FMEV-GFP) or the vector containing mut10 C/EBPα cDNA (FMEV-mut10). Transduction efficiencies obtained with BM cells are indicated. (D) Expression of the 30-kDa protein was confirmed by Western blot analysis. Protein extracts were prepared from either infected BM cells or transient transfected Phoenix packaging cells, from which virus supernatants were obtained. Protein (3 μg/lane) was separated by SDS-PAGE and immunoblotted with anti-C/EBPα antibody that detects an epitope on the C-terminus.