The E3 enzyme, also known as an E3 ubiquitin ligase, plays a crucial role in the process of ubiquitination, which is essential for protein regulation within cells. It facilitates the transfer of ubiquitin, a small protein, to target proteins, marking them for degradation or altering their function. This process is vital for maintaining cellular homeostasis and regulating various biological processes. E3 enzymes are part of a larger family of enzymes that include E1 (ubiquitin-activating enzymes) and E2 (ubiquitin-conjugating enzymes). They are highly specific, meaning each E3 enzyme typically targets specific substrates, influencing processes such as cell cycle regulation, DNA repair, and signal transduction. Their dysfunction can lead to various diseases, including cancer and neurodegenerative disorders.