Evolutionary conservation of a testes-specific proteasome subunit gene in Drosophila.
Proteasomes are large multisubunit particles that act as the proteolytic machinery for the ubiquitin-dependent proteolytic pathway. The core of this complex, the 20S proteasome, is made up of seven alpha-type and seven beta-type subunits, arranged in an (alpha1-alpha7)(beta1-beta7)(beta1-beta7)(alpha1-al pha7) configuration. Previous work had shown that there exist alternative isoforms of the Drosophila melanogaster alpha4-type subunit, encoded by two distinct genes, alpha4t1_dm and alpha4t2_dm, and that these are expressed exclusively in the germline of the testes. We sought to investigate the evolutionary conservation of this phenomenon by screening for orthologs of the alpha4-type gene family in the distantly related Drosophila species, D. virilis. We isolated the D. virilis orthologs of the somatically expressed gene, alpha4_dm, and the testes-specific gene, alpha4t2_dm. We failed to find an ortholog of the other testes-specific gene, alpha4t1_dm. The alpha4_dv gene maps to the X chromosome at 12A-C, its product shares 90% amino acid identity with alpha4_dm, and it is expressed at high levels in both males and females. The other gene, alpha4t_dv, encodes a protein most similar to the testes-specific alpha4t2_dm proteasome subunit (59% a.a. identity), and it maps to position 27 on chomosome 2. The expression of the alpha4t_dv gene is testes-specific, like that of alpha4t2_dm. The existence of testes-specific alpha4-type subunits in two widely diverged subgenera of Drosophila suggests that these subunit isoforms have important functional roles in spermatogenesis.
Department of Biology, Syracuse University, 130 College Place, Syracuse, NY 13244, USA. jbelote@mailbox.syr.edu
J M
JM
Belote
M
M
Miller
K A
KA
Smyth
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics; D003546:Cysteine Endopeptidases / Q000235:genetics*; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004330:Drosophila / Q000737:chemistry / Q000201:enzymology / Q000235:genetics*; D029721:Drosophila Proteins; D019143:Evolution, Molecular; D015870:Gene Expression / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D017344:Genes, Insect / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics*; D010802:Phylogeny; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012737:Sex Factors; D013737:Testis / Q000201:enzymology*
D029721:Drosophila Proteins; D009097:Multienzyme Complexes; D011506:Proteins; C113984:alpha4t-DV protein, Drosophila; D004247:DNA; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex