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. Author manuscript; available in PMC: 2014 Apr 17.
Published in final edited form as: Cell Rep. 2013 Sep 26;5(1):151–165. doi: 10.1016/j.celrep.2013.08.026

Figure 5.

Figure 5

Implications of alternative pathways for U1 and U2 addition.(A) Cotranscriptional pre-spliceosome formation.RNA polymerase II (RNAP) transcribes the5’ SS before the BS, providing U1 an opportunity to bind prior to U2, but this may not dictate which binds first to form the pre-spliceosome (see text).(B)Spliceosome cycle – 2013. Overall pathway foryeast spliceosome assembly, activationand splicing incorporating both U1→U2 and U2→U1 branches and known reversibilities(Hoskins et al., 2011; Tseng and Cheng, 2008).