The Biochemical Characterization of a Translational Repressor
Iron regulatory proteins (IRP) are crucial post-transcriptional regulators of iron metabolism. They influence the synthesis of proteins involved in iron uptake, storage and use by binding to their mRNAs. IRP1 stands out particularly with its ability to incorporate a [4Fe-4S] cluster to double function as the enzyme, cytosolic aconitase (c-acon). Since RNA binding and c-acon activity are mutually exclusive, the incorporation of this Fe-S cluster serves as a regulatory switch between the two forms that is dependent on iron availability in cells. This project aims to characterize the biochemical properties of IRP1 in order to understand the finely tuned translational regulation it performs. Polysome profiles were used to isolate different forms of IRP1 based on their presence in actively translating or repressed pools of mRNA. Functional assays like aconitase activity assays and RNA-binding assays were used for biochemical characterization of these forms. This study establishes baseline activities for these assays and also demonstrates that IRP1 differentially regulates the mRNAs of ferritin, the iron storage protein, and ferroportin, which exports iron from the cell. My research will allow further understanding of IRP1 as an agent of regulatory control.