Ubiquitin ligases are enzymes that play a crucial role in the process of protein degradation within cells. They attach a small protein called ubiquitin to target proteins, marking them for destruction by the proteasome, a cellular complex responsible for breaking down unwanted proteins. This tagging process is essential for regulating various cellular functions, including the cell cycle, DNA repair, and responses to stress. There are three main types of ubiquitin ligases: E1 (activating enzymes), E2 (conjugating enzymes), and E3 (ligating enzymes). The E3 ligases are particularly important because they determine the specificity of the ubiquitination process, deciding which proteins get tagged for degradation. This regulation is vital for maintaining cellular health and function.