We further demonstrate that the interactions between 5′UTRPab1 and Sbp1, which leads to the formation of the complex, are specific to each other. In a competition assay, the shifted band is efficiently outcompeted by an excess of unlabeled 5′UTRPab1 (Fig. 1C, lanes 3 and 4) but is not affected by an excess of unlabeled 5′UTRPab1-complement with nucleotide sequence complementary to 5′UTRPab1 (Fig. 1C, lanes 7 and 8). These results suggest that the observed band shifts are the result of formation of a specific, protein–RNA complex.