SDS-PAGE analysis of the UV light cross-linked RNA-protein complexes. (A) Characterization of the complexes formed by TH transcript (TH-tr), and by two EPO transcripts (NcoI-tr andDdeI-tr) and proteins (40 μg) from PC12 cells. Poly(U) RNA, TH HIPBS, or poly(C) RNA were added to the binding reaction as competitors (+ 50 ng, ++ 100 ng). Solid arrow points to the 50 kD complex. FP - free probe. (B) Comparison of complexes formed with the EPO DdeI transcript and protein factors from PC12 (lane 2), Hep3B (H3B, lane 3), and HepG2 (HG2, lane 4) before (lanes 2, 4, and 6) and after (lanes 3, 5, and 7) addition of 100 ng of poly(U) RNA. Lane 1 - free DdeI EPO probe. Solid arrow indicates the 50 kD complex. Open arrow indicates the 70 kD complex formed with extracts from Hep3B and HepG2 cells.