Binding of Sp1 to a non-canonical GC box downstream of the transcription start site.

<p>(<b>A</b>) Overview of oligonucleotides used for EMSA. LKB1 DSE: downstream element, position +35 to +65 within the LKB1 5′-UTR and the corresponding mutant (LKB1 DSE Mut). Sequences of oligonuceotides containing consensus sites of different transcription factors used for competition are given below. (<b>B</b>) The radioactively labeled LKB1 DSE was incubated with 4 µg of nuclear extracts obtained from “444” cells (lane 1) or HepG2 cells (lane 2–9). A 500-fold molar excess of indicated unlabeled competitor oligos was added (lanes 3–9) and separated in a 7% polyacrylamide gel. (<b>C</b>) Complex formation (Sp1 S) of the same probe with 4 µg of nuclear extracts from “444” cells (lane 1) or from HepG2 cells (lane 2–6) was self-competed by a 500-fold molar excess of wild-type oligo (WT; lanes 3) but not by a mutant oligo (LKB1 DSE MUT; lane 4). Addition of an antibody against Sp1 (sc-59 X) (lane 5) retarded the specific complex (Sp1 SS) while addition of an antibody against Sp 3 (lane 6) did not.