A. Schematic of phospho-dependent interaction of the spliceosomal AAR2 and PRP8. AAR2, a spliceosomal assembly protein, and PRP8 from a stable complex, that dissociates upon phosphorylation of AAR2. PPR8 is then free to bind the spliceosomal interaction partner protein BRR2 (Weber et al, 2013; Galej et al, 2013). This regulatory interaction switch is thought to be conserved between yeast and human. A protein kinase that can modulate the dissociation of AAR2 from PRP8 is unknown. 