Cdc34
Cdc34 is an essential ubiquitin-conjugating enzyme (E2) in the budding yeast Saccharomyces cerevisiae. It participates in the ubiquitination of substrates that are targeted by the SCF (Skp1–Cul1–F-box protein) ubiquitin ligase complex, marking them for degradation by the proteasome and thereby regulating progression through the cell cycle. The degradation of key regulators, such as the cyclin-dependent kinase inhibitor Sic1, is a central feature of Cdc34’s role in enabling the G1 to S phase transition.
Mechanistically, Cdc34 forms a thioester-linked ubiquitin intermediate via its active-site cysteine and transfers ubiquitin to substrates
Cdc34 homologs and related enzymes are conserved across eukaryotes, reflecting a core role in ubiquitin-mediated proteolysis