Fourth, results from our in-line probing experiments on 5′UTRPab1 alone (Fig. 2A) and the 5′UTRPab1–Sbp1 complex (Fig. 2B) show that the A-rich region in 5′UTRPab1 is protected upon the binding of Sbp1, indicating that this region in 5′UTRPab1 is likely to be the major binding site of Sbp1 (Supplemental Fig. 4). The measured Kd of Sbp1 and 5′UTRPab1 is 26.5 ± 1.1 nM. Templated poly(A)-rich tracts have been found in UTRs of many cellular mRNAs in eukaryotes including yeast and humans (Gilbert et al. 2007; Wigington et al. 2014). It is conceivable that Sbp1 likely binds to the A-rich region in these mRNAs in a similar way.