The U box is a modified RING finger - a common domain in ubiquitination.
Aravind
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Koonin
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EV
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D017874:Immediate-Early Proteins / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D029701:Saccharomyces cerevisiae Proteins; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*
D005656:Fungal Proteins; D018398:Homeodomain Proteins; D017874:Immediate-Early Proteins; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; C064658:RAG-1 protein; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; C051804:Vmw110 protein, Human herpesvirus 1; C114683:UFD2 protein, S cerevisiae