Evidence for a functional interaction between the Bari1 transposable element and the cytochrome P450 cyp12a4 gene in Drosophila melanogaster Rene ` Massimiliano Marsano a , Ruggiero Caizzi b , Roberta Moschetti b , Nikolaj Junakovic c, * a Dipartimento di Genetica, Universita ` di Parma, 43100 Parma, Italy b Dipartimento di Genetica e Microbiologia, Universita ` di Bari, 70126 Bari, Italy c Istituto di Biologia e Patologia Molecolari C.N.R, c/o Dipartimento di Genetica e Biologia Molecolare, Universita ` ‘‘La Sapienza’’, 00185 Roma, Italy Received 18 March 2005; received in revised form 22 June 2005; accepted 23 June 2005 Available online 1 August 2005 Received by W. Makalowski Abstract Previous studies of the genomic distribution of the transposon Bari1 in Drosophila melanogaster have revealed an element which is fixed at division 91F in over 90 lab and natural populations. Here we report about the structural and transcriptional features of the insertion site which was studied in sublines isolated from an exceptional Drosophila line polymorphic for the presence/absence of Bari1 at 91F. The insert is located at the 3V end of the cyp12a4 gene that belongs to the cytochrome P450 family. In flies with the insert the transcript of this gene encompasses 18 nucleotides of the transposon, it is shorter and is about tenfold more abundant compared to flies devoid of it. Although the hypothetical selective agent remains unknown, these data are suggestive of a selective advantage brought about by the Bari1 insert and are reminiscent of recent evidence for functional mutagenesis of cyp6g1, another P450 gene, brought about by Accord and Doc transposable elements in D. melanogaster and Drosophila simulans . D 2005 Elsevier B.V. All rights reserved. Keywords: Bari1 transposon; Fixed insertions; cyp12a4 gene; 3V end mRNA1 1. Introduction The contribution of transposable elements (TEs) to the evolution of their hosts has been debated for over two decades. A testable question in this matter is whether occasionally elements undergo fixation, possibly due to mutations beneficial to the host. The initial inability to find such elements has contributed to the selfish DNA hypoth- esis which posits that TEs are essentially parasitic (Charles- worth et al., 1994). Other authors, however, viewed hypothetical functional TE–host interactions as a dynamic process where detection of fixed elements depends on the timing of the interaction and the intensity of selective pressure. Ancient insertions may lose their identity due to point mutations and deletions thus turning undetectable with probes homologous to active transposons (Britten, 1997; Brosius, 1999; Fedoroff, 1999; Makalowski, 2000; Kidwell and Lisch, 2001; Petrov et al., 2003). For example, the analysis of genomic sequences has shown that a substantial fraction of human genes contains remnants of TE sequences in both regulatory and coding regions (Nekrutenko and Li, 2001; Jordan et al., 2003; van de Lagemaat et al., 2003). Recent beneficial insertions may fail to meet the fixation criterion as they are polymorphic for the presence/absence and may take a long time to reach fixation, depending on the selective advantage they confer. In the absence of these criteria, the only beneficial inserts detectable by in situ hybridization (the most popular approach in Drosophila) are 0378-1119/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.gene.2005.06.005 Abbreviations: DDT, 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane); EDTA, ethylenediamine tetraacetic acid; kb, kilobases; RACE, rapid amplification cDNA ends; SDS, sodium dodecyl sulphate. * Corresponding author. Tel.: +39 6 4991 2786; fax: +39 6 4991 2500. E-mail address: nikolaj.junakovic@uniroma1.it (N. Junakovic). Gene 357 (2005) 122 – 128 www.elsevier.com/locate/gene