FIG. 8.

Levels of LS3-interacting proteins correlate with c-Myc in fibroblast cell lines. (A) Nuclear extracts (50 μg) from HeLa (lane He), REF-myc (lane RM), and REF-neo (lane RN) cells blotted on nitrocellulose filters were renatured through guanidine hydrochloride and then hybridized in Southwestern binding buffer containing the α-³²P-labeled LS3 trimer oligonucleotide probe. c-Myc levels decrease from 90,000 copies of c-Myc protein in HeLa cells (49) to 30% of that level in REF-myc cells and 10% in REF-neo cells (35). Size markers (lane SM) are indicated. (B) Binding of the α-³²P-labeled LS3 trimeric probe to REF-myc and REF-neo nuclear extracts (10 μg) was compared in EMSA experiments. Binding conditions were identical to those used for experiments in previous figures. The indicated amounts of cold-competitor oligonucleotides (LS3 and SP1) were added in the designated lanes to evaluate the specificity of binding. A trimeric version of mutant oligonucleotide LS3-8 (mut) is included in lanes 4 and 9.