Post-transcriptional control of cytoskeletal proteins: How is tubulin expression regulated?

Introduction / Context:
Tubulin, a core cytoskeletal protein, is controlled by feedback mechanisms that couple protein assembly status to mRNA stability. This ensures homeostasis of microtubule components within the cell.

Given Data / Assumptions:

• Cells monitor unassembled (soluble) tubulin levels.
• Tubulin expression is tuned at the post-transcriptional level.
• Mechanisms can involve mRNA stability and translation efficiency.

Concept / Approach:
Autoregulatory control: unassembled tubulin promotes the binding of a protein complex that recognizes nascent tubulin mRNAs, leading to their destabilization or translational repression. When tubulin is incorporated into microtubules, the signal diminishes, stabilizing tubulin mRNAs and allowing synthesis to restore balance.

Step-by-Step Solution:
Identify that the feedback signal is the pool of free tubulin.Free tubulin promotes mRNA destabilization via protein–mRNA interactions.Therefore, regulation occurs by binding of tubulin (directly or via associated factors) to tubulin mRNA.

Verification / Alternative check:
Drug-induced microtubule depolymerization elevates free tubulin and reduces tubulin mRNA, consistent with autoregulation; polymerization has the opposite effect.

Why Other Options Are Wrong:

• Alternative splicing only: Not the principal, rapid feedback mechanism.
• Binding to finished polypeptide: Feedback acts at mRNA level rather than product–product binding.
• Direct DNA binding by tubulin: Tubulin is not a transcription factor.
• miRNA exclusively: miRNAs may contribute but do not explain classic autoregulation.

Common Pitfalls:
Assuming all gene regulation is transcriptional; tubulin regulation is a model for mRNA-level control.

Final Answer:
By binding of tubulin protein to tubulin mRNA (autoregulatory mRNA control).