A gene encoding a ubiquitin-fusion protein was isolated from a cDNA library made from the intersegmental muscles (ISM) of the moth, Manduca sexta. The predicted amino acid sequence of this fusion protein is highly conserved when compared to the sequence of homologous proteins from diverse species. The Manduca clone encoding this ubiquitin fusion gene hybridized with a single, abundantly expressed transcript in all tissues examined. In the ISM, the transcript was present at high levels, independent of the developmental stage or hormonal treatment of these muscles. Data from other species indicate that ubiquitin-fusion genes participate in ribosome biogenesis.