What is the primary function of the protein ubiquitin in cellular processes?

A To regulate gene expression
B To mark proteins for degradation ✓
C To facilitate protein folding
D To transport molecules across cell membranes

Explanation

Ubiquitin is a small protein that tags other proteins for degradation by the proteasome, a process known as ubiquitination.

Source

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