EPO transcripts containing HIPBS-like sequence form ribonucleoprotein complexes with protein extracts from Hep3B and HepG2 that migrate with the same mobility as the TH mRNA-associated complex. (A) RNA gel-shift assay with TH transcript (TH-tr, lanes 1 to 2) and PC12 cells extract (10 μg), EPO BglII transcript (EPOBglII-tr, lanes 3 to 5), EPO DdeI transcript (EPO DdeI-tr, lanes 6 to 8), and EPO oligoribonucleotide (EPO-HIPBS, lanes 9 to 11) and with proteins (40 μg) from Hep3B (H3B) and HepG2 (HG2) cells. Solid arrow indicates the main, faster-migrating complex. Open arrow indicates the second, slower-migrating complex, visible only when EPO transcripts are used. FP - free probe. Free probes migrate only in lanes 1, 3, 6, and 9. Note that less PC12 protein extract was used in the binding reaction with the TH transcript to obtain autoradiographically comparable signal between TH and EPO complexes. (B) Competition of the complexes formed by EPO DdeI transcript with proteins (40 μg) from Hep3B (lanes 1 to 4) or Hep2G (lanes 5 to 8) by TH HIPBS (lanes 2 and 6) or poly(C) RNA (lanes 3 and 7) but not by poly(U) RNA (lanes 4 and 8). Solid arrow indicates specific complex. Open arrow indicates slower-migrating complex.