It has been shown that the first two RRM domains of the Pab1 bind to the polyadenosine sequence in the 5′UTRPab1 with nanomolar affinity (Sachs et al. 1987; Kessler and Sachs 1998), which contributes to the mechanism of an autoregulated translation of Pab1 mRNA in vitro and in vivo (de Melo Neto et al. 1995; Bag and Wu 1996; Hornstein et al. 1999). The apparent Kd of the 5′UTRPab1 and Pab1 is 31.2 ± 2.5 nM (Supplemental Fig. S3), which is slightly higher compared to that obtained on a 5′UTRPab1–Sbp1 complex (26.5 ± 1.1 nM) under the same experimental conditions.