DUPLICATED PROTEASOME SUBUNIT GENES IN DROSOPHILA-MELANOGASTER ENCODING TESTES-SPECIFIC ISOFORMS

Using the previously cloned proteasome alpha-type subunit gene Pros28. 1, we screened a Drosophila melanogaster genomic library using reduced stringency conditions to identify closely related genes. Two new gene s, Pros28.1A (map position 92F) and Pros28.1B (map position 60D7), sho wing high sequence similarity to Pros28.1, were identified and charact erized. Pros28.1A encodes a protein with 74% amino acid identity to PR OS28.1, while the Pros28.1B gene product is 58% identical. The Pros28. 1B gene has two introns, located in exactly analogous positions as the two introns in Pros28.1, while the Pros28.1A gene lacks introns. Nort hern blot analysis reveals that the two nerv genes are expressed only in males, during the pupal and adult stages. Tissue-specific patterns of expression were examined using transgenic flies carrying lacz-fusio n reporter genes. This analysis revealed that both genes are expressed in germline cells during spermatogenesis, although their expression p atterns differed. Pros28.1A expression is first detected at the primar y spermatocyte stage and persists into the spermatid elongation phase of spermiogenesis, while Pros28.1B expression is prominent only during spermatid elongation. These genes represent the most striking example of cell-type-specific proteasome gene expression reported to date in any system and support the notion that there is structural and functio nal heterogeneity among proteasomes in metazoans.