Which of the following posttranslational modifications marks a protein for degradation?

• A. Phosphorylation
• B. Ubiquitination
• C. Signal Sequences
• D. Protein Cleavage

Answer: (B)

Verified step by step guidance

1. Understand the concept of posttranslational modifications: These are chemical changes to a protein after it has been synthesized, which can affect the protein's function, location, or stability.
2. Identify the role of ubiquitination: Ubiquitination is a process where a small protein called ubiquitin is attached to a substrate protein, marking it for degradation by the proteasome, a protein complex that breaks down proteins.
3. Differentiate between the options: Phosphorylation involves adding a phosphate group, which typically regulates protein activity or function, not degradation. Signal sequences direct proteins to specific locations in the cell. Protein cleavage involves cutting the protein, which can activate or deactivate it, but not necessarily mark it for degradation.
4. Recognize that ubiquitination is specifically known for targeting proteins for degradation, making it distinct from the other modifications listed.
5. Conclude that ubiquitination is the posttranslational modification that marks a protein for degradation, as it signals the proteasome to degrade the tagged protein.