The octamer motif present in the Rex-1 promoter binds Oct-1 and Oct-3 expressed by EC cells and ES cells.

Rex-1 is a zinc finger-containing gene that is expressed in embryonal carcinoma (EC) cells and embryonic stem (ES) cells. Upon differentiation with retinoic acid (RA), transcription of the Rex-1 gene decreases rapidly. Analysis of the 5'-flanking region of the Rex-1 gene identified a consensus motif for the octamer family of transcription factors that stimulates expression from the Rex-1 promoter. In this report, we utilized gel mobility shift analysis to examine the binding of transcription factors to the Rex-1 octamer motif. F9 EC cells, D3 ES cells, and human NT2/D1 EC cells each from at least two prominent DNA/protein complexes with the octamer motif. Supershift analysis identifies Oct-1 and Oct-3 in these complexes. When F9 EC cells are induced to differentiate by treatment with RA for 48 h, there is a complete loss of the DNA/protein complex containing Oct-3. In contrast, the other DNA/protein complexes, including the DNA/protein complex containing Oct-1, can still be detected. These results provide support for a role of Oct-3 in the transcription of the Rex-1 gene.