Two genes become one: the genes encoding heterochromatin protein Su(var)3-9 and translation initiation factor subunit eIF-2gamma are joined to a dicistronic unit in holometabolic insects.
The Drosophila suppressor of position-effect variegation Su(var)3-9 encodes a heterochromatin-associated protein that is evolutionarily conserved. In contrast to its yeast and mammalian orthologs, the Drosophila Su(var)3-9 gene is fused with the locus encoding the gamma subunit of translation initiation factor eIF2. Synthesis of the two unrelated proteins is resolved by alternative splicing. A similar dicistronic Su(var)3-9/eIF-2gamma transcription unit was found in Clytus arietis, Leptinotarsa decemlineata, and Scoliopterix libatrix, representing two different orders of holometabolic insects (Coleoptera and Lepidoptera). In all these species the N terminus of the eIF-2gamma, which is encoded by the first two exons, is fused to SU(VAR)3-9. In contrast to Drosophila melanogaster, RT-PCR analysis in the two coleopteran and the lepidopteran species demonstrated the usage of a nonconserved splice donor site located within the 3' end of the SU(VAR)3-9 ORF, resulting in removal of the Su(var)3-9-specific stop codon from the mRNA and complete in-frame fusion of the SU(VAR)3-9 and eIF-2gamma ORFs. In the centipede Lithobius forficatus eIF-2gamma and Su(var)3-9 are unconnected. Conservation of the dicistronic Su(var)3-9/eIF-2gamma transcription unit in the studied insects indicates its origin before radiation of holometabolic insects and represents a useful tool for molecular phylogenetic analysis in arthropods.
Krauss
V
V
Institute of Genetics, Martin Luther University Halle-Wittenberg, D-06108 Halle, Germany. krauss@rz.uni-leipzig.de
Reuter
G
G
D000595:Amino Acid Sequence; D000818:Animals; D001181:Arthropods / Q000235:genetics; D001483:Base Sequence; D017931:DNA Primers; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics; D015852:Eukaryotic Initiation Factor-2 / Q000737:chemistry / Q000235:genetics*; D019143:Evolution, Molecular; D005091:Exons; D017344:Genes, Insect; D006570:Heterochromatin / Q000235:genetics*; D007313:Insecta / Q000235:genetics; D007915:Lepidoptera / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D021122:Protein Subunits; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D017931:DNA Primers; D029721:Drosophila Proteins; D015852:Eukaryotic Initiation Factor-2; D006570:Heterochromatin; D021122:Protein Subunits; D012097:Repressor Proteins; C089148:Su(var)3-9 protein, Drosophila