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. Author manuscript; available in PMC: 2016 Apr 20.
Published in final edited form as: Annu Rev Genet. 2015 Oct 2;49:339–366. doi: 10.1146/annurev-genet-112414-054639

Figure 2.

Figure 2

Possible modes of Upf1 recruitment and activation during nonsense-mediated mRNA decay (NMD). Four different modes of Upf1 recruitment and activation during NMD are described. (a) Upf1 recruitment and activation based on the EJC (exon junction complex) model. (b) Upf1 recruitment and activation based on the Upf1 3′-UTR (untranslated region) sensing and potentiation model. (c) Upf1 recruitment and activation based on the faux 3′-UTR model. (d) Upf1 recruitment and activation based on stochastic binding of Upf1 and activation by Upf2 and Upf3 binding only at a premature termination codon. Abbreviations: CBP, cap-binding protein; PABPC1, poly(A)-binding protein.