Figure 4.

Proposed model for alternative splicing of the FER1 HCH mRNA precursors mediated by IRP. Iron overabundance directs the conversion of IRP to a form with no RNA-binding activity (aconitase). This would leave the intron containing the IRE accessible for excision. Both spliced and unspliced messages would be produced constitutively, but high iron availability would shift the equilibrium toward the spliced messages. In addition, the use of two alternative polyadenylation sites would result in four mature mRNAs.