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Aminoacyl-tRNA synthetases are a class of enzymes which charge tRNAs with their cognate amino acids. Asparaginyl-tRNA synthetase (NARS) is localized to the cytoplasm and is a member of the class II family of tRNA synthetases. The N-terminal domain characterizes the signature sequence for the eukaryotic asparaginyl-tRNA synthetases.

Ubiquitin-conjugating enzyme E2 H (UBE2H) is a member of the ubiquitin-conjugating enzyme family. Protein modification with ubiquitin is a vital cellular apparatus for directing abnormal or short-lived proteins for degradation. Ubiquitination requires at least 3 classes of enzymes: ubiquitin-activating enzymes (E1s) ubiquitin-conjugating enzymes (E2s) and ubiquitin-protein ligases (E3s). UBE2H receives ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. UBE2H protein sequence is 100% identical to the mouse homolog and 98% identical to the frog and zebrafish homologs.

UBE2D1 is a member of the ubiquitin-conjugating enzyme family. Ubiquitination involves at least 3 classes of enzymes: ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s) and ubiquitin-protein ligases (E3s). UBE2D1 is strongly related to a stimulator of iron transport (SFT), and is up-regulated in hereditary hemochromatosis. In addition, UBE2D1 functions in the ubiquitination of the tumor-suppressor protein p53 and the hypoxia-inducible transcription factor HIF1alpha by interacting with the E1 ubiquitin-activating enzyme and the E3 ubiquitin-protein ligases.

GLUL catalyzes the synthesis of glutamine from glutamate and ammonia. Glutamine is a major source of energy and that takes part in cell proliferation, inhibition of apoptosis, and cell signaling. GLUL is expressed during early fetal stages, and has a role in maintaining body pH by removing ammonia from circulation. Mutations in GLUL gene are related with congenital glutamine deficiency.

GLUL catalyzes the synthesis of glutamine from glutamate and ammonia. Glutamine is a major source of energy and that takes part in cell proliferation, inhibition of apoptosis, and cell signaling. GLUL is expressed during early fetal stages, and has a role in maintaining body pH by removing ammonia from circulation. Mutations in GLUL gene are related with congenital glutamine deficiency.

DARS uses a 2 step reaction to catalyze the specific attachment of an amino acid to its cognate tRNA: the amino acid (AA) is first activated by ATP to form AA-AMP and then transferred to the acceptor end of the tRNA.

Phosphopantothenate-cysteine ligase (PPCS) catalyzes the first step in the biosynthesis of coenzyme A (CoA) from pantothenic acid (vitamin B5), which is a vital universal pathway in prokaryotes and eukaryotes. PPCS, being one of the last enzymes in this pathway, converts phosphopantothenate to phosphopantothenoylcysteine.

Ubiquitin Conjugating Enzyme E2Z, also known as UBE2z, is a protein coding gene which is a part of the ubiquitin-conjugating enzyme family. UBE2z catalyzes the covalent attachment of ubiquitin to various proteins. UBE2z takes part in in apoptosis regulation and is also a specific substrate for UBA6, not charged with ubiquitin by UBE1.

UBE2D3 enzymes are human homologs of the yeast UBC4/5 family and play many important regulatory roles in inflammation and cancer. UbcH5a mediates the degradation of a myriad of short-lived regulatory proteins (such as p53 in the presence of E6/E6-AP or MDM2, c-Fos, I?B?, p105) and abnormal proteins. UBE2D3 has 88% and 89% sequence identity with UbcH5a and UbcH5b respectively.

UBE2D2 belongs to the E2 ubiquitin-conjugating enzyme family. UBE2D2 takes part in the ubiquitination of the tumor-suppressor protein p53, which is induced by an E3 ubiquitin-protein ligase. UBE2D2 catalyzes ubiquitination of IkB-alpha in a SCFB-TRCP and phosphorylation dependent method.

UBE2E1 belongs to the E2 ubiquitin-conjugating enzyme family. UBE2E1 accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. UBE2E1 catalyzes the covalent attachment of ISG15 to other proteins. UBE2E1 mediates the selective degradation of short-lived and abnormal proteins. In vitro, UBE2E1 also catalyzes 'Lys-48'-linked polyubiquitination.

UBE2E3 or Ubiquitin-conjugating enzyme E2 E3 is part of the E2 ubiquitinconjugating enzyme family. UBE2E3 is needed for the destruction of mitotic cyclins and for cell cycle progression. The ubiquitination process covalently attaches to a short protein of 76 amino acids called ubiquitin, to a lysine residue on the target protein. When a protein has been tagged with one ubiquitin molecule, other rounds of ubiquitination form a polyubiquitin chain that is recognized by the proteasome's 19S regulatory particle, triggering the ATP-dependent unfolding of the target protein which grants passage into the proteasome's 20S core particle, where proteases degrade the target into short peptide fragments for recycling by the cell.

This E2 enzyme encodes for the human homolog of the yeast DNA repair gene RAD6, which is induced by DNA damaging agents. UBE2B can conjugate ubiquitin to histone H2A in an E3- independent manner in vitro, and is essential for the multi-ubiquitination and degradation of N-end rule substrates. Additionally, UBE2B may have a role in sepsis-induced muscle protein proteolysis and cancer-induced cachexia.

GARS is an (alpha)2 dimer which is a member of the class II family of tRNA synthetases. GARS is a glycyl-tRNA synthetase, one of the aminoacyl-tRNA synthetases which charge tRNAs with their cognate amino acids. GARS catalyzes the attachment of glycine to tRNA(Gly). In addition, GARS is able to produce diadenosine tetraphosphate (Ap4A), which is a universal pleiotropic signaling molecule required for cell regulation pathways, by direct condensation of two ATPs. GARS has been demonstrated to be a target of autoantibodies in the human autoimmune diseases, polymyositis or dermatomyositis.

UBE2W receives ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. In vitro, UBE2W catalyzes monoubiquitination and 'Lys-11'-linked polyubiquitination. UBE2W is broadly expressed, particularly at highest levels in the testis.

E3 ubiquitin-protein ligase RNF181 (RNF181) accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the thioester form and subsequently directly transfers the ubiquitin to targeted substrates. RNF181 is widely expressed, with the highest levels in the liver and heart and the lowest levels in the brain and skeletal muscle. RNF181 is also expressed in platelets (at protein level).

UBE2L6 belongs to the E2 ubiquitin-conjugating enzyme family. UBE2L6 enzyme is very similar in its primary structure to the enzyme encoded by UBE2L3 gene. UBE2L6 catalyzes the covalent attachment of ubiquitin to other proteins. UBE2L6 functions in the e6/e6-ap-induced ubiquitination of p53/tp53.

Ubiquitin-conjugating enzyme E2S (UBE2S) belongs to the ubiquitin-conjugating enzyme family. UBE2S is able to form a thiol ester linkage with ubiquitin in a ubiquitin activating enzyme-dependent manner, a typical property of ubiquitin carrier proteins. UBE2S catalyzes the covalent attachment of ubiquitin to other proteins. UBE2S acts as a crucial factor of the anaphase promoting complex/cyclosome (APC/C), which is a cell cycle-regulated ubiquitin ligase that controls progression through mitosis. UBE2S acts by purposely elongating 'Lys-11'-linked polyubiquitin chains initiated by the E2 enzyme UBE2C/UBCH10 on APC/C substrates, augmenting the degradation of APC/C substrates by the proteasome and promoting mitotic exit. UBE2S also acts by elongating ubiquitin chains initiated by the E2 enzyme UBE2D1/UBCH5 in vitro; it is nevertheless uncertain whether UBE2D1/UBCH5 acts as an E2 enzyme for the APC/C in vivo. UBE2S is also involved in ubiquitination and consequent degradation of VHL, resulting in an accumulation of HIF1A.

Human Ubquitin Conjugating Enzyme 9 (Ubc9) is a member of the E2 family and is specific for the conjugation of SUMO to a variety of target proteins. SUMO conjugation to target proteins is mediated by a different, but analogous, pathway to ubiquitinylation. This E2 is unusual in that it interacts directly with protein substrates that are modified by sumolyation, and may play a role in substrate recognition. Ubc9 can mediate the conjugation of SUMO-1 to a variety of proteins including RanGAP1, I?B?, and PML without the requirement of an E3 ligase.

UBE2N belongs to the E2 ubiquitin-conjugating enzyme family. UBE2N catalyzes the ATP-dependent synthesis of non-canonical polyubiquitin chains, a process which doesn’t set in motion proteasomal degradation. UBE2N mediates the transcription of some target genes and is believed to have a role in cell cycle progression; cellular differentiation and DNA repair mechanisms which ensure cell survival after DNA damage.

UbcH10 is an essential mediator of mitotic destruction events and cell cycle progression. It catalyzes the destruction of cyclins A and B in conjunction with the anaphase-promoting complex, and therefore, plays an important role in the control of the cell exit from mitosis This activity is essential at then end of mitosis for the inactivation of their partner kinase Cdc2 and exit from mitosis into G1 of the next cell cycle. In addition, UbcH10 bears homology to yeast PAS2, a gene that is essential for biogenesis of peroxisomes. UbcH10 is useful for in vitro ubiquitinylation reactions.

GLUL catalyzes the synthesis of glutamine from glutamate and ammonia. Glutamine is a major source of energy and that takes part in cell proliferation, inhibition of apoptosis, and cell signaling. GLUL is expressed during early fetal stages, and has a role in maintaining body pH by removing ammonia from circulation. Mutations in GLUL gene are related with congenital glutamine deficiency.

The alteration of proteins with ubiquitin is a vital cellular mechanism for targeting atypical or short-lived proteins for degradation. Ubiquitination involves noT less than three classes of enzymes: ubiquitin-activating enzymes, or E1s, ubiquitin-conjugating enzymes, or E2s, and ubiquitin-protein ligases, or E3s. UBE2A is part of the E2 ubiquitin-conjugating enzyme family. UBE2A is necessary for post-replicative DNA damage repair. UBE2A catalyzes the covalent attachment of ubiquitin to other proteins. UBE2A is necessary for postreplication repair of UV-damaged DNA.