Correct Option: C

Ubiquitination is an enzymatic, protein post-translational modification (PTM) process in which the carboxylic acid of the terminal glycine from the di-glycine motif in the activated ubiquitin forms an amide bond to the epsilon amine of the lysine in the modified protein. Ubiquitination, also known as ubiquitylation, ubiquitylation, regulates degradation of cellular proteins by the ubiquitin-proteasome system, controlling a protein’s half-life and expression levels. This process involves the sequential action of ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligases (E3). The reaction catalyzed by each enzyme transfers a covalent bond with ubiquitin from one enzyme to the next and finally to a target protein. ​