The enzymes of the ubiquitylation pathway play a pivotal role in a number of cellular processes including regulated and targeted proteasomal degradation of substrate proteins. Three classes of enzymes are involved in the process of ubiquitylation; activating enzymes (E1s), conjugating enzymes (E2s) and protein ligases (E3s). UBE2B is a member of the E2 ubiquitin-conjugating enzyme family and cloning of the human gene was first described by Koken et al. (1991). UBE2B shares 70% identity with its yeast homologue but lacks the acidic C-terminal domain. The ring finger proteins RAD5 and RAD18 interact with UBE2B and other members of the RAD6 pathway (Notenboom et al., 2007; Ulrich and Jentsch, 2000). In complex UBE2B and RAD18 trigger replication fork stalling at DNA damage sites during the post replicative repair process (Tsuji et al., 2008). Null mutations of the UBE2B gene in mice are associated with structural abnormalities in sperm and SNP analysis of human UBE2B variants has provided evidence for association of this gene with male infertility (Escalier et al., 2003; Suryavathi et al., 2008).
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