DNA binding and transactivating properties of the paired and homeobox protein pax4

Transcription factors Pax-4 and Pax-6 are known to be key regulators of pan creatic cell differentiation and development. We report on the cloning of a mouse Pax-4 gene, which contains 10 exons, spanning a 4.7-kbp region. The gene-targeting experiments revealed that Pax-4 and Pax-6 cannot substitute for each other in tissue with overlapping expression of both genes. We iden tified DNA-binding specificities of Pax-4 paired domain and paired-type hom eodomain. Despite the different Pax-4 amino acid residues in positions resp onsible for Pax-6 paired-domain specificity, the DNA-binding specificities of Pax-4 and Pax-6 are similar. The Pax-4 homeodomain was shown to preferen tially dimerize on DNA sequences consisting of an inverted TAAT motif, sepa rated by 4-nucleotide spacing. The Pax-4 transactivation domain was localiz ed within its C-terminal region, which transactivated GAL-based reporter 2. 5-fold less than the C-terminal region of Pax-g. We believe that Pax-4 can act as a Pax-6 "repressor," due to the competition for binding sites and lo wer transactivation potential of Pax-4. (C) 1999 Academic Press.