Localization of HMG-I binding region. (A) Detection of an HMGI(Y)-like protein by BG1 probe from nuclear extracts of A20-2J cells. Competition with increasing amounts (30- and 100-fold molar excess) of unlabeled G region oligonucleotide shows specificity of the retarded band. (B) Recombinant human HMGI(Y) protein binds only to theHindIII-SalI probe (sequence shown in Fig 3) derived from the regulatory region. HindIII-XhoI probe containing ISRE was unable to bind rhHMGI(Y) protein. Competition with unlabeled G region oligonucleotide inhibited the complex in a dose-dependent fashion.