PBX and PREP homeoproteins bind to the P0- pax6b PA2 element and with PDX1 to the P0- pax6b PA1 element. (A) EMSAs were performed on PA1 probe of pax6b (PA1b) using nuclear extract of pancreatic TU6 cells. 10 ng of unlabeled oligonucleotides PA1b, UE-A or mutated UE-A (sequences depicted below the lanes) were added as competitor, as indicated above the lanes. Position of complexes T', T, L and S are indicated by the arrows. (B) EMSAs were performed on PA2 probe of pax6b (PA2b) using nuclear extract of pancreatic TU6 cells. 10 ng of unlabeled oligonucleotides PA2b (sequence depicted below the lanes), PA1b, UE-A or mutated UE-A were added as competitor. Position of complexes L and S are indicated by the arrows. Abbreviations: PBX1a and PREP1, in vitro-translated PBX1a and PREP1 proteins; PDX1, recombinant PDX1; PDX1 Ab, PDX1 antiserum; PBXL. Ab, antiserum recognizing specifically the long PBX isoforms (PBX1a, PBX2, and PBX3a) (Santa Cruz Biotechnology); PREP1 Ab, PREP1 antibody; nsp., nonspecific complex, Ret. lysate, reticulocyte lysate.