Transcription factors of the ONECUT class possess a single cut domain and a divergent homeodomain. They regulate gene networks by controlling the expression of other transcription factors and they play an important role in cell differentiation and metabolism. We identified earlier in mammals HNF-6 (ONECUT-1), the founding member of the class, and ONECUT-2 (OC-2). We have now characterized in the mouse a third ONECUT member, which we call OC-3. Its gene is located on chromosome 10. The sequence of OC-3 (490 residues) displays 51% amino acid identity with HNF-6 and 50% with OC-2. OC-3 has a DNA-binding specificity similar to that of HNF-6 and it is a stimulator of gene transcription. OC-3 mRNA is found in brain, stomach, and upper intestine in the adult and embryonic mouse. Our earlier work on HNF-6 and the expression patterns of the three mammalian ONECUT genes suggest that they all participate to the control of organ development from the foregut and midgut endoderm. (C) 2002 Elsevier Science (USA).