E3 ubiquitin ligases are enzymes that play a crucial role in the process of protein degradation within cells. They facilitate the transfer of ubiquitin, a small protein, to target proteins, marking them for destruction by the proteasome. This process is essential for regulating various cellular functions, including the cell cycle, DNA repair, and responses to stress. These ligases are known for their specificity, as they can recognize and bind to particular substrates. There are several families of E3 ligases, each with unique mechanisms and functions, contributing to the complexity of cellular regulation and maintaining protein homeostasis.