To study how the 5′UTRPab1 folds and which region in the RNA binds to Sbp1, we determined the secondary structures of 5′UTRPab1 and 5′UTRPab1–Sbp1 complex using in-line probing (Soukup and Breaker 1999). In-line probing is an RNA structure analysis technique that uses the relative flexibility of RNA backbone conformation to determine secondary structure characteristics of the RNA. As shown in Figure 2, in the absence of Sbp1, the A-rich region in the 5′UTRPab1 adopts a single-stranded conformation (Fig. 2A). Addition of Sbp1 protects the degradation of the RNA in this region (Fig. 2B), suggesting that the protein binds to the A-rich sequence in the 5′UTRPab1 (Supplemental Fig. S4).