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. 2014 Aug 7;55(3):467–481. doi: 10.1016/j.molcel.2014.05.031

Figure 7.

Figure 7

Model for the Coordination of Transcription Termination with RNA Degradation at NNS Targets

(A) The NNS complex interacts with the Ser5P form of the CTD via the CID of Nrd1p and with the nascent RNA (boxes indicate recognition motifs for the Nrd1-Nab3 heterodimer), which defines a termination form of the complex (orange shaded).

(B) Concomitantly with or subsequently to dissociation of the elongation complex by Sen1p, Trf4p interacts with the CID of Nrd1p, replacing the CID-CTD interaction and allowing the release of Nrd1p-Nab3p from RNAPII.

(C) Polyadenylation of the transcript by TRAMP (in the presence or absence of Mtr4p) is stimulated by the simultaneous interaction of Nrd1p-Nab3p with the RNA and with Trf4p. Trf4p also might recruit the exosome via the interaction with Rrp6p, possibly favoring subsequent degradation of the transcript in a polyadenylation- independent manner. The alternative interaction of Nrd1p with Trf4p (instead of the CTD) defines a degradation form of the NNS complex (yellow shaded) that might or might not contain Sen1p.