How does ubiquitin attach to target proteins, and which amino acid is primarily involved?

• A. Ubiquitin attaches through an amide linkage to the R group of lysine.
• B. Ubiquitin attaches through a hydrogen bond to the R group of serine.
• C. Ubiquitin attaches through a disulfide bond to the R group of cysteine.
• D. Ubiquitin attaches through an ionic bond to the R group of arginine.

Answer: (A)