Before It Gets Started: Regulating Translation at the 5′ UTR
Translational regulation by RNA binding proteins. (a) In iron-deficient cells, IRPs bind to the IRE localized in the 5′ UTR of ferritin mRNA, blocking its translation. Once cellular iron levels increase, a complex containing Fe binds to IRPs. Thus, these proteins are allosterically modified, which reduces IRP-IRE binding and allows the translation of ferritin mRNAs. (b) msl-2 gene regulation in females flies. After transcription in the nucleus, SXL specifically binds to intronic U-rich regions of msl-2 pre-mRNA and inhibits the intron removal (1). In the cytoplasm, SXL binds to the same elements localized now in the 5′ UTR of mature msl-2 mRNA, enhances the translation initiation of a upstream ORF (2), and prevents the main ORF translation (3). The regulatory elements in the 3′ UTR of msl-2 mRNA were not represented.
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