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. 2008 Nov 28;283(48):33199–33210. doi: 10.1074/jbc.M802935200

FIGURE 4.

FIGURE 4.

FBI-1 binds to the proximal Sp1-binding GC-box 2, and Sp1 binds to the distal FRE3 element in vitro. FBI-1 and Sp1 compete with each other for binding to FRE3 and GC-box 2. A, comparisons of the nucleotide sequences of the FREs and Sp1-binding GC-boxes with their consensus sequences. B, EMSA. FBI-1ZFDBD was incubated with FRE4 or the typical Sp1 GC-box probe. FBI-1 binds to the Sp1-binding GC-box probe. FRE4, control FBI-1 binding probe. Sp1 GC-box, a typical Sp1-binding oligonucleotide probe with 5′-GGGCGGGG-3′ core sequence. C, EMSA. Recombinant Sp1ZFDBD or FBI-1ZFDBD was incubated with the GC-box probes. Sp1 binds both GC-box 1 and 2, but binds more strongly to GC-box 2 (lanes 2 and 7). FBI-1 binds to the Sp1 GC-box 2 probe only. D, EMSA and identification of a new Sp1 binding element, FRE3. Recombinant Sp1ZFDBD (0.1 μg) was incubated with the FRE probes or the GC-box probes. Sp1 significantly binds to FRE3 and GC-box 2 probes. E, EMSA. FBI-1 and Sp1 compete for binding to FRE3 and GC-box 2 in vitro. The probes were incubated with Sp1ZFDBD (0.1 μg) in the presence of increasing amounts of FBI-1ZFDBD (0.1, 0.4, and 0.8 μg). FBI-1 competes with Sp1 for binding to FRE3 and GC-box 2 in vitro.