While our data strongly suggest a synergistic model described, we cannot, however, rule out a competitive binding of Sbp1 and Pab1 on the same RNA. Since both proteins can bind to the polyadenosine or A-rich sequences, they could potentially compete for the same target sequences. In this scenario, RNA remodeling is also likely to be accompanied when one protein replaces the other. Pab1 contains four tandem RRMs in which the first two RRM domains mediate the polyadenosine RNA binding (Sachs et al. 1987; Kühn and Pieler 1996; Deo et al. 1999; Safaee et al. 2012). Furthermore, a stretch of the RNA containing 12 consecutive adenosines or longer is required for a high affinity binding to Pab1 (Sachs et al. 1987). On the other hand, in the case of Sbp1, we showed that the protein mainly binds to the A-rich sequence in the RNA cooperatively using multiple domains, especially the two RRM domains flanking the central RGG repeats. Thus, the distinctive RRM domain architecture in Pab1 and Sbp1 will most likely lead to different conformations when these two proteins interact with the same RNA and, as a result, remodel the RNA structure differently. A related question is whether Sbp1 prefers binding to specific transcripts containing poly(A) or perhaps even the same transcript in different stages of mRNA biogenesis, considering that Sbp1 also binds to mRNA sequences other than poly(A) (Mitchell et al. 2013; Wang et al. 2016). Clearly, further studies involving genomic and structural investigations are required to answer these questions.