The concentration of iron in a cell is an important regulator of gene expression. Explain two mechanisms through which iron concentration regulates gene expression in mammalian cells

Question

What will be an ideal response?

Answer 1

Answer: One mechanism through which iron concentration can control gene expression is through post-transcriptional control of translation. Ferritin, an iron-storage protein, is synthesized when iron concentrations in the cell are high. At the 5? untranslated end of the ferritin mRNA is a 28-nucleotide sequence call the iron-response element (IRE) that forms a hairpin loop. This loop binds to the IRE-binding protein when iron concentrations are low and prevents translation of the ferritin mRNA. When iron is present in high concentrations, the IRE-binding protein binds to iron and no longer binds the IRE sequence, allowing ribosomes to access and translate the ferritin mRNA. Another way that iron regulates gene expression is through modulation of mRNA stability. Synthesis of the iron uptake protein transferrin receptor is stimulated when iron concentrations inside the cell are low. In this case the IRE is in the 3? untranslated region of the transferrin receptor mRNA. When iron concentrations are low, an IRE-binding protein binds to the 3? IRE and prevents the degradation of the mRNA, resulting in more translation and increased transferrin receptor protein expression. With high iron levels, binding of the IRE-binding protein is decreased and the transferrin receptor mRNA is degraded more rapidly.