Hemin Controlled Translational Repressor (HCR) is a regulatory protein that acts as a post-transcriptional repressor of gene expression in response to the presence of hemin, an iron-containing molecule. HCR binds to specific RNA sequences, known as iron-responsive elements (IREs), located in the untranslated regions (UTRs) of target messenger RNAs (mRNAs).
When hemin concentrations are low, HCR is unable to bind to the IREs, allowing translation of the target mRNAs to occur. However, in the presence of hemin, HCR undergoes a conformational change that enables it to recognize and bind to the IREs. This binding prevents ribosomes from efficiently accessing the mRNA, inhibiting protein synthesis.
The HCR-mediated translational repression is a crucial mechanism for regulating the expression of genes involved in iron homeostasis, heme biosynthesis, and other iron-related processes. By suppressing protein production when hemin is abundant, HCR helps prevent excessive accumulation of iron in cells, which can lead to oxidative damage and other detrimental effects.
HCR is commonly found in various organisms, including bacteria, yeast, and higher eukaryotes, indicating its evolutionary conservation and importance in cellular iron metabolism. Its role as a translational repressor offers a fine-tuning mechanism for maintaining appropriate iron levels within cells and adapting to changing iron conditions in the environment.
