description
Ubiquitin monomers are processed from larger precursors and then activated by formation of a thiol ester bond between ubiquitin and a cysteine residue of an E1 activating enzyme (UBA1 or UBA6, Jin et al. 2007). The ubiquitin is then transferred to the active site cysteine residue of an E2 conjugating enzyme (reviewed in van Wijk and Timmers 2010, Kleiger and Mayor 2014, Stewart et al. 2016). Precursor proteins containing multiple ubiquitin monomers (polyubiquitins) are produced from the UBB and UBC genes. Precursors containing a single ubiquitin fused to a ribosomal protein are produced from the UBA52 and RPS27A genes. The proteases OTULIN and USP5 are very active in polyubiquitin processing, whereas the proteases UCHL3, USP7, and USP9X cleave the ubiquitin-ribosomal protein precursors yielding ubiquitin monomers (Grou et al. 2015). Other enzymes may also process ubiquitin precursors. A resultant ubiquitin monomer is activated by adenylation of its C-terminal glycine followed by conjugation of the C-terminus to a cysteine residue of the E1 enzymes UBA1 or UBA6 via a thiol ester bond (Jin et al. 2007, inferred from rabbit homologues in Haas et al. 1982, Hershko et al. 1983). The ubiquitin is then transferred from the E1 enzyme to a cysteine residue of one of several E2 enzymes (reviewed in van Wijk and Timmers 2010, Stewart et al. 2016)

external resources
NCBI:1457809
REACTOME:R-HSA-8866652
PUBMED:26235645
PUBMED:24457024
PUBMED:27002219
PUBMED:17597759
PUBMED:19940261
PUBMED:6277905
PUBMED:6305978

genes
CDC34 , UBE2K , RPS27A , UBA52 , UBB , UBC , UBA1 , UBE2A , UBE2B , UBE2D1 , UBE2D2 , UBE2E1 , UBE2G1 , UBE2G2 , UBE2H , UBE2L3 , UCHL3 , USP7 , USP5 , USP9X , UBE2E3 , UBE2C , UBE2S , UBE2T , UBE2R2 , UBA6 , UBE2W , UBE2Z , OTULIN , UBE2Q2 ,