The mouse genome contains two expressed intronless retroposed pseudogenes for the sentrin/sumo-1/PIC1 conjugating enzyme Ubc9

The ubiquitin conjugating (ubc) E2 enzyme ubc-9 conjugates the ubiquitin-li ke peptide sentrin/SUMO-1/PIC1 to target proteins which include the Fas ant igen. We show that the mouse genome contains four copies of the ubc-9 gent. These include a structural ubc-9 gene consisting of seven exons which enco de a protein identical to human ubc-9, and three intronless processed pseud ogenes. The open reading frames (ORF) of two of the pseudogenes, ubc9-psi 1 and ubc9-psi 2, correspond to the cDNA of ubc-9 and encode for proteins wh ich differ from ubc9 by three and one amino acid substitutions respectively . The third pseudogene, ubc9-psi 3, contains many mutations and stop codons . ubc9-psi 1 and ubc9-psi 2 are flanked by 5'- and 3'-untranslated (UT) reg ions homologous to those of the structural ubc-9 gene. Both gents contain a polyA tail and direct repeats at both ends suggesting that they arose by m RNA retroposition. Both ubc9-psi 1 and ubc9-psi 2 are transcribed into mRNA in murine cells. In contrast to ubc9, the protein products of ubc9-psi 1 a nd ubc9-psi 2 fail to bind Fas and to complement an yeast conditional ubc9 mutant. These results suggest that ubc9-psi 1 and ubc9-psi 2 encode for pro teins that may interact with targets that differ from those recognized by u bc-9. (C) 1999 Elsevier Science Ltd. All rights reserved.