CDC34 is an E2 ubiquitin-conjugating enzyme that plays a critical role in protein degradation and cell cycle regulation. The enzyme accepts ubiquitin from E1 activating enzymes and catalyzes its covalent attachment to target proteins via E3 ligase complexes 1. CDC34 utilizes distinct structural domains for its function: a core catalytic domain containing the active site cysteine and a unique C-terminal acidic tail domain that is essential for substrate ubiquitination but not E3 binding 2. The enzyme employs separate sites to coordinate initial ubiquitin attachment to substrates and subsequent polyubiquitin chain assembly 1. CDC34 targets multiple substrates including transcriptional repressors ICERIIgamma and ATF5, leading to their degradation and derepression of cAMP-induced transcription 3. In cancer contexts, CDC34 is overexpressed in hepatocellular carcinoma and associated with poor prognosis 4. Recent studies demonstrate CDC34's role in immune evasion, where it stabilizes HIF1α to upregulate CD47 expression, helping cancer cells evade macrophage phagocytosis and predicting poor response to immune checkpoint inhibitors 5. These findings highlight CDC34's dual role in normal cell cycle control and cancer progression.