Figure 8.

Illustration of mechanistic models for the stimulatory functions of PTB in 3′ end processing. (a) PTB and 3′ end cleavage. We propose that PTB facilitates the binding of hnRNP H to the DGRS located at the AUX-DSE, which in turn, stimulates the assembly of the 3′ end cleavage machinery through the recruitment of CstF or PAP. (b) PTB and polyadenylation. We propose that PTB stabilizes the association of hnRNP H with a UGRS located upstream of the pA signal where it can increase the processivity of PAP. Black arrows indicate the functional interactions shown in this study while the grey arrow refers to the previously reported ability of hnRNP H to increase CstF binding to the DSE element (14,15,17–19).