The PRAT Purine Synthesis Gene Duplication in Drosophila melanogaster and Drosophila virilis Is Associated with a Retrotransposition Event and Diversification of Expression Patterns

摘要

The Drosophila melanogaster Prat genenencodes amidophosphoribosyltransferase (PRAT;nEC 2.4.2.14), which performs the first step in de novonpurine nucleotide synthesis. Prat mutations have anrecessive lethal phenotype that is found for otherngenes encoding enzymes in this pathway. The D.nmelanogaster genome project has revealed a secondngene, CG10078 or Prat2, encoding a protein with 76%namino acid sequence identity with Prat. The twongenes map to different arms of chromosome 3 andnhave different intron/exon organizations, as we confirmednby cDNA sequence analysis of Prat2. With thengoal to determine the functional significance of thisngene duplication, we isolated and sequenced twonPRAT-encoding genes from Drosophila virilis. Wenfind that the two D. virilis genes are orthologous tonthe two D. melanogaster genes in terms of intronexon organization, amino acid coding sequence, andn5￠ noncoding sequence. The absence of introns innboth DmelPrat and DvirPrat genes suggests that Pratnoriginated from a retrotransposition of Prat2 andnthat the gene duplication has been preserved in thentwo species since their divergence approximately 40nmillion years ago. Analysis of mRNA expression inndevelopment shows that maternal expression, detectednin adult ovaries and embryos prior to the onsetnof zygotic transcription, is present for Prat but notnPrat2 in both species. Taken together, these findingsnsupport the notion that two PRAT-encoding genesnhave evolved distinct functions in both Drosophilanspecies.