RING finger, H2 subclass, found in ubiquitin-protein ligase E3-alpha-1 (UBR1), E3-alpha-2 (UBR2), and similar proteins
Two UBR family members, UBR1 and UBR2, are major N-recognin ubiquitin ligases that both function in the N-end rule degradation pathway. They can recognize substrate proteins with type-1 (basic) and type-2 (bulky hydrophobic) N-terminal residues as part of N-degrons and an internal lysine residue for ubiquitin conjugation. They also function in a quality control pathway for degradation of unfolded cytosolic proteins. Their action is stimulated by Hsp70. Moreover, UBR1 and UBR2 are negative regulators of the leucine-mTOR signaling pathway. Leucine might activate this pathway in part through inhibition of their ubiquitin ligase activity. In yeast, only one E3, encoded by UBR1, mediates the recognition of substrates by the N-end rule pathway. Saccharomyces cerevisiae UBR1 also functions as an additional E3 ligase in the endoplasmic reticulum-associated protein degradation (ERAD). It can provide ubiquitin ligation activity for the ERAD substrate mutated Ste6 (sterile). Schizosaccharomyces pombe UBR1 is a critical regulator that influences the oxidative stress response via degradation of active Pap1 basic leucine zipper (bZIP) transcription factor in the nucleus. Both UBR1 and UBR2 contain an N-terminal ubiquitin-recognin (UBR) box involved in binding type-1 (basic) N-end rule substrate, an N-domain (also known as ClpS domain) required for type-2 (bulky hydrophobic) N-end rule substrate recognition, a C3H2C3-type RING-H2 finger, and a C-terminal UBR-specific autoinhibitory (UAIN) domain.
Comment:C3H2C3-type RING-H2 finger consensus motif: C-X2-C-X(9-39)-C-X(1-3)-H-X(2-3)-H-X2-C-X(4-48)-C-X2-C, where X is any amino acid and the number of X residues varies in different fingers
Comment:A RING finger typically binds two zinc atoms, with its Cys and/or His side chains in a unique "cross-brace" arrangement.
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