STRUCTURE AND EXPRESSION OF THE DROSOPHILA UBIQUITIN-80-AMINO-ACID FUSION-PROTEIN GENE

In the fruitfly Drosophila, as in all eukaryotes examined so far, some ubiquitin-coding sequences appear fused to unrelated open reading fra mes. Two of these fusion genes have been previously described (the hom ologues of UBI1-UBI2 and UBI4 in yeast), and we report here the organi zation and expression of a third one, the DUb80 gene (the homologue of UBI3 in yeast). This gene encodes a ubiquitin monomer fused to an 80- amino-acid extension which is homologous with the ribosomal protein en coded by the UBI3 gene. The 5' regulatory region of DUb80 shares commo n features with another ubiquitin fusion gene, DUb52, and with the rib osomal protein genes of Drosophila, Xenopus and mouse. We also find he lix-loop-helix protein-binding sequences (E-boxes). The DUb80 gene is transcribed to a 0.9 kb mRNA which is particularly abundant under cond itions of high protein synthesis, such as in ovaries and exponentially growing cells.