Formation of the ribonucleoprotein complex associated with EPO HIPBS-like oligoribonucleotide. (A) Gel-shift analysis of the binding reaction of EPO oligoribonucleotide and protein factors from HepG2 cells. EPO oligoribonucleotide is sufficient to form a complex with proteins from HepG2 cells (lane 1). Formation of this complex is prevented by competition with 100 ng of cold EPO (lane 2) or TH HIPBS (lane 3) oligoribonucleotides, EPO DdeI transcript (lane 4), or poly(C) RNA (lane 5). (B) Analysis of the EPO oligoribonucleotide-protein complex after UV light cross-linking and SDS-PAGE. EPO oligoribonucleotide forms a 50 to 55 kD complex with cytoplasmic proteins from HepG2 cells (lane 1). Formation of this complex is abolished by competition with 100 ng of poly(C) RNA (lane 2) or TH HIPBS (lane 3). (C) Gel-shift analysis of complexes formed by proteins from HepG2 cells and wild-type (wt) or mutated (M-1, 2, 3, 4) EPO HIPBS. Bracket indicates the specific complex. (D) Gel-shift analysis of the HepG2 protein complex associated with EPO HIPBS in the presence of increasing concentrations of RT1 (lanes 1 to 4). Bracket indicates the specific complex. FP-freeprobe