When iron is not available, E. coli can stop synthesis of all proteins, such as superoxide dismutase and succinate dehydrogenase, that require iron. Describe a mechanism for this regulation.

Verified step by step guidance

1. Understand that E. coli regulates protein synthesis in response to iron availability to conserve resources and maintain cellular function.
2. Recognize that the key regulatory protein involved is the Iron Regulatory Protein (IRP) or the Ferric Uptake Regulator (Fur) in bacteria, which senses intracellular iron levels.
3. When iron is scarce, Fur is inactive and cannot bind to DNA, leading to the derepression of genes involved in iron acquisition and the repression of genes encoding iron-containing proteins.
4. This regulation occurs at the transcriptional level, where Fur binds to specific DNA sequences called Fur boxes in the presence of iron, repressing transcription of iron uptake genes and allowing expression of iron-containing proteins only when iron is available.
5. Thus, when iron is not available, Fur-mediated repression of iron-containing protein genes like superoxide dismutase and succinate dehydrogenase prevents their synthesis, conserving iron for essential functions.

Key Concepts

Iron-Dependent Regulation in Bacteria

Bacteria like E. coli regulate gene expression based on iron availability to conserve resources and maintain homeostasis. When iron is scarce, they suppress synthesis of iron-requiring proteins to prioritize essential functions and avoid toxic effects of free iron.

Fur (Ferric Uptake Regulator) Protein

Fur is a transcriptional repressor that binds iron and regulates genes involved in iron metabolism. In iron-rich conditions, Fur-iron complex binds DNA to repress target genes; when iron is low, Fur cannot bind DNA, leading to derepression or activation of iron acquisition and repression of iron-using proteins.

Post-Transcriptional Regulation via Small RNAs

Small regulatory RNAs (sRNAs), such as RyhB in E. coli, mediate iron-dependent regulation by binding mRNAs of iron-containing proteins, promoting their degradation or inhibiting translation. This mechanism allows rapid downregulation of iron-requiring proteins during iron starvation.