Analysis of PAB1135 interaction with 21-mer RNA oligonucleotides in vitro. (A) Electrophoretic mobility shift assays with different radiolabeled RNA probes incubated with increasing amounts of purified protein. 50, 100, 200 or 400 pmol of PAB1135 were incubated with 1 pmol of either poly-rU8C5A8 (lanes 2-5), poly-rC8U5G8 (lanes 7-10), or poly-rUUA/C (lanes 12-15) at 37°C for 30 min. RNA-protein complexes were fractionated on 8% native polyacrylamide gels and visualized by phosphorimaging. PAB1135 binds poly-rC8U5G8 efficiently. -, no protein added to the reaction. Free structured and unstructured RNA oligos and PAB1135-RNA complexes are indicated on the right-hand side. (B) Quantitation of bands visualized in RNA binding assay. The ratio of protein-bound RNA over free RNA in each lane was calculated for the four different amounts of PAB1135 (50, 100, 200 or 400 pmol).