Figure 6.
Model: three-layered control of pA tail length in S. cerevisiae. Polyadenylation carried out by the CPF/CF IA/CF IB complex (dark gray) is primarily terminated by Nab2p (green), whose association with the mRNP (dark line and light-gray shapes depicting proteins and RNA, respectively) produces ∼60-A-long pA tails (light yellow). If Nab2p is not available, either the nuclear pool of Pab1p (blue) or the CPF complex, together with the cleavage factors CF IA and CF IB (highlighted in dark yellow at this step), provides a fail-safe termination of polyadenylation, producing longer pA tails.
