Function
Ubiquitin activating enzyme (Uba) or E1 enzyme catalyzes the first step in the ubiquitination of a protein tagged to be degraded by the proteasome.  Ubiquitin activating enzyme (E1) and ATP produce a C-terminal acyl adenylated ubiquitin molecule which binds to ubiquitin conjugating enzyme (E2) (Ubc) cysteine[1].  The Ubc then binds to ubiquitin ligase (E3) via a conserved binding region.  E3 catalyzes the transfer of ubiquitin from the Ubc-ubiquitin complex to a lysine residue of the target protein.  
- Uba1 see Uba1.
 
- Uba3 is the catalytic subunit of NEDD8 activating enzyme and APPB1 is its regulatory subunit.  Similar to ubiquitin and SUMO, NEDD8 binds to proteins after processing of its C-terminal.  
 
- Uba6 regulates the interferon-gamma production of T-cells by modulating NF-κB activation pathway[2].
- Uba7 is involved in interferon-stimulated gene 15 conjugation[3].
For ubiquitin-like modifier-activating enzyme Atg7 see Autophagy-related protein
 (PDB entry 1y8x). .
 References
- ↑ Nagai Y, Kaneda S, Nomura K, Yasuda H, Seno T, Yamao F. Ubiquitin-activating enzyme, E1, is phosphorylated in mammalian cells by the protein kinase Cdc2. J Cell Sci. 1995 Jun;108 ( Pt 6):2145-52. PMID:7673335 
- ↑ Lee JY, An EK, Hwang J, Jin JO, Lee PCW. Ubiquitin Activating Enzyme UBA6 Regulates Th1 and Tc1 Cell Differentiation. Cells. 2021 Dec 29;11(1):105. PMID:35011668 doi:10.3390/cells11010105
- ↑ Lin M, Li Y, Qin S, Jiao Y, Hua F. Ubiquitin-like modifier-activating enzyme 7 as a marker for the diagnosis and prognosis of breast cancer. Oncol Lett. 2020 Apr;19(4):2773-2784. PMID:32218830 doi:10.3892/ol.2020.11406