THE EVOLUTION OF SMALL GENE CLUSTERS - EVIDENCE FOR AN INDEPENDENT ORIGIN OF THE MALTASE GENE-CLUSTER IN DROSOPHILA-VIRILIS AND DROSOPHILA-MELANOGASTER

We analyzed a 5,770-bp genomic region of Drosophila virilis that conta ins a cluster of two maltase genes showing sequence similarity with ge nes in a cluster of three maltase genes previously identified in Droso phila melanogaster. The D, virilis maltase genes are designated Mav1 a nd Mav2. In addition to being different in gene number, the cluster of genes in D. virilis differs dramatically in intron-exon structure fro m the maltase genes in D. melanogaster; the transcriptional orientatio n of the genes in the cluster also differs between the species. Our fi ndings support a model in which the maltase gene cluster in D. virilis and D. melanogaster evolved independently. Furthermore, while in D. m elanogaster the maltase gene cluster lies only 10 kb distant from the larval cuticle gene cluster, the maltase and larval cuticle gene clust ers in D. virilis are located very far apart and on a different chromo some than that expected from the known chromosome arm homologies betwe en D. virilis and D. melanogaster. A region of the genome containing t he maltase and larval cuticle gene clusters appears to have been reloc ated between nonhomologous chromosomes.