Polyadenylation releases mRNA from RNA polymerase II in a process that is licensed by splicing

Cartoons of the presumptive 3′-terminal EDC and of the CPA. (A) Assembly of the 3′-terminal EDC (Berget 1995; Sharma et al. 2008). Only the core factors required for poly(A) site cleavage and 3′-terminal exon definition are labeled. The CPA is shown in green, and the splicing factors that interact with the CPA, and presumably combine with it to form the 3′-terminal EDC, are shown in yellow. RNA polymerase II is shown in blue. The diagram accommodates the following known protein–protein and protein–RNA interactions: CFI_m with U2AF (Millevoi et al. 2006); CPSF with U2 snRNP (Kyburz et al. 2006); CFII_m and CstF with the CTD, with CPSF and with each other (Murthy and Manley 1995; de Vries et al. 2000; Fong and Bentley, 2001; Qu et al. 2006; Zhang and Gilmour, 2006); CFI_m with CFII_m and CPSF (Ruegsegger et al. 1996; de Vries et al. 2000; Venkataraman et al. 2005); and U2AF, U2 snRNP, CFI_m, CPSF, and CstF with the RNA (Zhao et al. 1999; Black, 2003; Brown and Gilmartin, 2003; Venkataraman et al. 2005). The placement of U2AF on the CTD of RNA polymerase II is arbitrary but is based on the fact that U2AF has been shown to bind tightly to the polymerase (Robert et al. 2002; Ujvari and Luse, 2004) except when the polymerase is isolated by use of a CTD-binding antibody which might displace the U2AF from the CTD (Das et al. 2007). SR proteins are not shown. (B) The EDC after poly(A) site cleavage. Poly(A) polymerase (PAP) is shown in this panel, interacting with CPSF (Kaufmann et al. 2004). PAP also interacts with U2AF (Vagner et al. 2000) and CFI_m (Kim and Lee, 2001), but these interactions are not shown because of difficulties of depiction in two dimensions. The DNA oligo used for RNaseH-cutting in Figure 2B and later experiments is shown. (C) The CPA after poly(A) site cleavage.