= Solution
The extract forms a slower-migrating labelled complex. Addition of either anti-<TCF transcription factor> or anti-<HNF1β> replaces much of the lower shifted band with an even slower species. \b[The results support participation of both <TCF transcription factor> and <HNF1β> in promoter-associated complexes], assuming the <antibodies> are specific. The separate supershifts are consistent with their presence together, but cannot exclude two unresolved, similarly migrating complexes containing one factor each. They do not by themselves establish direct binding of each factor to its own predicted motif, physical interaction between the factors, or occupation of the native promoter in intact <biological cells>. Mutant binding sites, purified components and a chromatin-occupancy assay address those distinct claims.
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