Question

Intracellular proteins are targeted for proteolytic degradation in proteasomes upon conjugation with

• A. ubiquitin
• B. integrin
• C. peptidase
• D. calreticulin

Hint:

- "Ubiquitin tag = Death tag" for proteins.
- Proteasomes degrade only ubiquitinated proteins.
- Important in protein quality control and cell cycle regulation.

Answer 1

The Correct Option is A

Step 1: Proteasome-mediated protein degradation is a selective process.
Step 2: Proteins meant for degradation are tagged with ubiquitin, a small regulatory protein. This process is called \textit{ubiquitination}.
Step 3: Ubiquitin-tagged proteins are recognized and degraded by the 26S proteasome complex.
Step 4: Other options: Integrin is a cell adhesion molecule, peptidase is an enzyme that hydrolyzes peptides, and calreticulin is a calcium-binding chaperone protein. None of these are involved in proteasome targeting.
Final Answer: Ubiquitin is the correct answer.
\[\boxed{\text{Correct Answer: (A)}}\]