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. 2012 Oct 1;26(19):2119–2137. doi: 10.1101/gad.200303.112

Figure 5.

Figure 5.

The CTD facilitates different termination mechanisms for protein-coding and noncoding genes. (A) Poly(A)-dependent termination pathway. RNA is cleaved by 3′ end processing factors at the polyadenylation site. The CTD with Ser2-P is involved in recruiting factors, including Pcf11, Rtt103, p54/PSF, and Sen1, to facilitate termination of long polyadenylated transcripts. Pcf11 and Rtt103 are required for the recruitment of exoribonuclease Rat1 in yeast, while Xrn2 is recruited by p54/PSF in humans. Sen1 (Senataxin in humans) may function on some of these genes by resolving RNA–DNA hybrids. (B) Nrd1c-dependent termination pathway. The Nrd1 complex (Nrd1–Nab3–Sen1) interacts via Nrd1 with the CTD phosphorylated on Ser5, which is present at the 3′ ends of short genes, such as snoRNAs and CUTs. Ssu72 and Ess1 are also required to dephosphorylate Ser5-P, although the exact mechanism of Nrd1c-dependent termination awaits further studies.