Fig. 4. Electrophoretic mobility shift assays. Top panel shows the sequences of the oligonucleotides 37/38 and the competitors 37/38 A, B and C used in the assay. The oligo 37/38 contains sequences between residues 543 and 581 including the two putative GAGA binding sites (underlined) at positions 548 and 558 (Fig. 7). The competitor sequences are identical to oligo 37/38 except for the residues replaced with Ts. The lower panel shows the results from EMSA when radioactively labeled 37/38 oligonucleotide was used as probe and incubated with embryonic nuclear extracts in the absence or in the presence of unlabeled competitors (Materials and Methods). Lane 1: oligo 37/38 forms three shifted bands (arrows) in the absence of competitors. Lane 2: 37/38 competitor. The three bands are competed. Lane 3: ADF competitor (non-specific sequence). No competition is observed. Lane 4: oligo 37/38 A as a competitor. The bottom two bands (connected arrows) are competed. Lane 5: 37/38 B competitor. The top band (arrow) is competed. Lane 6: 37/38 C competitor. All three bands are competed. Summary: the top band is competed by sequences included in the left third of the 37/38 oligo and the bottom two bands are competed by sequences in the middle third of the 37/38 oligo. No protein binds to the right third of the oligo 37/38. The results are schematically shown in Fig. 7.