Transcription factor C/EBPalpha: novel sites of expression and cloning of the human gene.

We describe the characterization of recombinant clones for the human transcription factor CCAAT/enhancer binding protein alpha (hC/EBP alpha). The intronless hC/EBP alpha gene is almost 90% homologous to its rat and mouse counterparts. The gene copies of more distant species are less conserved, but the alignment reveals a striking homology in five regions, of which four may be involved in transactivation functions while the fifth concerns the carboxy-terminal bZip sequences (basic region and leucine zipper) mediating sequence specific DNA-binding. In addition to the usual expression sites, significant transcript levels were detected in the epidermal compartment of human skin and in rat aorta by northern analysis. The presence of hC/EBP alpha is further documented by immunohistochemical analysis of human skin biopsies and cultured keratinocytes showing the nuclear presence of the protein, notably in the suprabasal layers of the epidermis and in human keratinocytes induced to differentiate.