Gel mobility shift analysis of the α₂ integrin core promoter. (A) Gel mobility shift analysis was performed with the ³²P-end–labeled double-stranded DNA fragment containing the core promoter region (bp −30 to −92) and 1 μg of nuclear protein from uninduced or K562 cells (K562) induced for 4 days (4d Ind) or 8 days (8d Ind) with phorbol dibutyrate. The two major DNA-protein complexes are indicated with arrows. (B) Binding of nuclear proteins from uninduced and induced K562 cells to the 62-bp core fragment is specific. DNA-proteins are formed in the absence of competitive inhibitor (⊘) or in the presence of unlabeled specific inhibitor (Unlab) or a nonspecific (NS) inhibitor consisting of 119-bp double-stranded DNA fragments from the coding region of the α₂ cDNA. Gel mobility shift analysis was performed as described in Materials and Methods. The DNA-protein interaction formed with the α_IIb integrin silencer domain is indicated with a dash. Gel mobility shift analysis using the α_IIb silencer domain served as a positive control for nuclear extracts.