Figure 7. The location of mutants that disrupt splicing suggests a similarity to exon-definition in mammalian splicing.

A. Spliceosome assembly in mammalian systems is thought to occur via exon-definition, where interactions between U1 and U2 snRNP components across an internal exon, or CPSF components and U2 snRNP across a terminal exon, are necessary for efficient processing of the upstream intron. B. Functional location of a subset of the mutants examined in this work, presented on a model transcript. Factors shown in red caused a statistically significant increase in the precursor levels of at least one transcript in our screen, whereas those in grey did not affect the splicing of any of the transcripts.