Ancient origin of animal U-box ubiquitin ligases.
BACKGROUND
The patterns of emergence and diversification of the families of ubiquitin ligases provide insights about the evolution of the eukaryotic ubiquitination system. U-box ubiquitin ligases (UULs) are proteins characterized by containing a peculiar protein domain known as U box. In this study, the origin of the animal UUL genes is described.


RESULTS
Phylogenetic and structural data indicate that six of the seven main UUL-encoding genes found in humans (UBE4A, UBE4B, UIP5, PRP19, CHIP and CYC4) were already present in the ancestor of all current metazoans and the seventh (WDSUB1) is found in placozoans, cnidarians and bilaterians. The fact that only 4-5 genes orthologous to the human ones are present in the choanoflagellate Monosiga brevicollis suggests that several animal-specific cooptions of the U box to generate new genes occurred. Significantly, Monosiga contains five additional UUL genes that are not present in animals. One of them is also present in distantly-related protozoans. Along animal evolution, losses of UUL-encoding genes are rare, except in nematodes, which lack three of them. These general patterns are highly congruent with those found for other two families (RBR, HECT) of ubiquitin ligases.


CONCLUSIONS
Finding that the patterns of emergence, diversification and loss of three unrelated families of ubiquitin ligases (RBR, HECT and U-box) are parallel indicates that there are underlying, linage-specific evolutionary forces shaping the complexity of the animal ubiquitin system.
Marín
Ignacio
I
Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Científicas, Valencia, Spain. imarin@ibv.csic.es
D048868:Adaptor Proteins, Signal Transducing / Q000145:classification / Q000235:genetics; D000818:Animals; D056897:Choanoflagellata / Q000235:genetics; D045643:DNA Repair Enzymes / Q000145:classification / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D009687:Nuclear Proteins / Q000145:classification / Q000235:genetics; D010802:Phylogeny; D000072260:RNA Splicing Factors; D025521:Tumor Suppressor Proteins / Q000145:classification / Q000235:genetics; D043743:Ubiquitin-Protein Ligase Complexes / Q000145:classification / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000145:classification* / Q000235:genetics*
D048868:Adaptor Proteins, Signal Transducing; D009687:Nuclear Proteins; D000072260:RNA Splicing Factors; D025521:Tumor Suppressor Proteins; C431153:UBOX5 protein, human; D043743:Ubiquitin-Protein Ligase Complexes; C467728:STUB1 protein, human; C486451:UBE4A protein, human; C473697:UBE4B protein, human; D044767:Ubiquitin-Protein Ligases; D045643:DNA Repair Enzymes; C417041:PRPF19 protein, human