PBX-PREP dimers bind to the P0- pax6b PC1 element and PDX1 binds to PC3b as a monomer. (A) EMSAs were performed on PC1 probe of pax6b (PC1b) using nuclear extract of pancreatic TU6 cells. (B) EMSAs were performed on PC3 probe of pax6b (PC3b) using nuclear extract of pancreatic TU6 cells. 10 ng of unlabeled oligonucleotides PC3b, UE-A and mutated UE-A were added as competitor. Abbreviations: PBX1a and PREP1, recombinant PBX1a and PREP1 proteins produced in vitro in a reticulocyte extract; PDX1 Ab, PDX1 antiserum; PBXL. Ab, antiserum recognizing specifically the long PBX isoforms (PBX1a, PBX2, and PBX3a) (Santa Cruz Biotechnology); PREP1 Ab, PREP1 antibody PBX1a and PREP1; P.I. serum, pre-immune serum.