To test the possibility of a direct interaction between Sbp1 and the 5′UTRPab1, purified Sbp1 (Supplemental Fig. S2A) and in vitro-transcribed 5′UTRPab1 were combined and their interactions were examined by EMSA. As shown in Figure 1B, a complex is formed when Sbp1 and 5′UTRPab1 are combined. Multiple bands are not seen at higher protein concentrations, suggesting that binding of Sbp1 and 5′UTRPab1 is at 1:1 stoichiometry.