(61) THE DROSOPHILA MELANOGASTER MITOCHONDRIAL PORIN GENE LOCALIZED ON THE CHROMOSOME 2L AT REGION 32B3-4: SEQUENCE, EXPRESSION PATTERN AND MUTANT ANALYSIS

Marta Oliva, Angela Messina and Vito De Pinto
Istituto di Scienze Biochimiche e Farmacologiche, Facolte di Scienze M.F.N., Universite di Catania, viale A. Doria, 6, 95125 Catania, ITALIA

The cDNA encoding mitochondrial porin in Drosophila melanogaster was used as a probe for screening a genomic library. We sequenced a 4494 bp genomic region which contained the whole gene for the mitochondrial porin or VDAC. It was found that this D.m. porin gene contains five exons, numbered IA (115 bp), IB (123 bp), II (320 bp), III (228 bp) and IV (752 bp). The exons II, III and IV contain the protein coding sequence and the 3Ġ untranslated sequence (3ĠUTR). The first base in exon II precisely corresponds to the first base of the starting ATG codon. Exon IA corresponds to the 5ĠUTR sequence reported in the published cDNA sequence. Exon IB corresponds to an alternative 5ĠUTR sequence, demonstrated to be transcribed by 5ĠRACE experiments. The exon-intron splicing borders and the length of the exon III perfectly match an homologous internal exon detected in the mouse genes. Such exon encodes a protein domain predicted by sequence transmembrane arrangement models to contain major hydrophilic loops and it is thus suspected to have a conserved distinct function. In situ hybridization experiments confirmed the localization of the genomic clone on the chromosome 2L at region 32B3-4. Together with genomic Southern blotting at various stringencies, the same experiment did not confirm the presence of a second genetic locus on D. melanogaster chromosomes. Northern blots demonstrated that the porin gene is an housekeeping one: three messages of approx. 1.2-1.6 kbp are transcribed in every fly developmental stage that was studied. They were shown to derive by an alternative usage of different promoters and polyadenylation sites. Known lethal mutants are very rare in 32B region. We anyway found one, containing a P element. Its analysis is presently in progress and the results will be presented.

Acknowledgements: The authors acknowledge the support from Telethon, Italy (grant 711 to VDP).