RNA Polymerase II Elongation at the Crossroads of Transcription and Alternative Splicing

Figure 2

Alternative models for the “first come, first served” mechanism of splice site selection. (a) Fast elongation promotes usage of the stronger downstream 3′ splice site. (b) Slow elongation causes preferential excision of the upstream intron (first served = first excised). (c) Slow elongation causes commitment to E33 inclusion via recruitment of splicing factors (first served = first committed). Both introns are excised individually and in an order that is independent of elongation. (Based on [38].)