What is the primary mechanism by which the ubiquitin-proteasome pathway regulates protein degradation?

A Tagging proteins with ubiquitin for recognition by the proteasome ✓
B Cleaving peptide bonds in proteins to release amino acids
C Modifying protein structure to prevent aggregation
D Inhibiting protein synthesis to reduce protein levels

Explanation

The ubiquitin-proteasome pathway is a major mechanism for regulating protein degradation, where proteins are tagged with ubiquitin for recognition and degradation by the proteasome.

Source

Alberts et al., Molecular Biology of the Cell
Protein Metabolism Biochemistry Protein Degradation Medium MEDICAL Confidence: high