The intersex (ix) gene works in concert with doublesex (dsx) at the bottom of the sexdetermination hierarchy to control somatic sexual differentiation in Drosophila melanogaster females. Here we report the isolation and characterization of the Drosophila intersex (ix) homologue in the pest lepidopteron Maruca vitrata (Mvix). The Mvix gene exhibits major complexity with respect to the Drosophila homolog. It is expressed in males and females and its pre-mRNA is subject to differential splicing events which affect both the protein coding and the non-coding regions. Moreover, Northern blot experiments revealed the presence of a femalespecific transcript in pupae RNA, which appears to be the first described sex specific transcript of ix homologs characterized to date. The expression of Mvix cDNA in D.melanogaster transgenic flies indicates that the MvIX product, which shares a relatively high degree of homology with the D.melanogaster IX protein, is able to partially rescues the Drosophila mutant phenotype.

We report the characterization of two novel genes of Drosophila melanogaster, named mst36Fa and mst36Fb. They define a novel gene family, showing identical time and tissue-specificity limited to male germ cells where their transcription starts during meiotic prophase. These two genes encode for two slightly basic proteins highly homologous to each other and fairly rich in leucine and glutamic acid. Although strictly clustered, these genes utilize different promoter regions as revealed by examination of transgenic flies bearing mst36F-promoter-lacZ reporter constructs and by reverse transcription-polymerase chain reaction assays. Our data suggest that at least one gene (mst36Fa) of the cluster is under translational repression until spermiogenesis suggesting a putative role in the spermatides differentiation. The present study is aimed at the structural analysis of these genes.

The rDNA magnification process consists of a rapid and inheritable rDNA increase occurring in bobbed males: in a few generations the bb loci acquire the wild-type rDNA value and reach a bb+ phenotype.—We have analyzed the rDNA magnification process in the repair-recombination-deficient mutant mei9a, both at the phenotypical and rDNA content levels. In mei9a bb double mutants the recovery of bb+ phenotype is strongly disturbed and the rDNA redundancy value fails to reach the wild-type level. The strong effect of this meiotic mutation on rDNA magnification suggests a close relationship between this phenomenon and the repair-recombination processes.

The Pre-intermoult gene-1 (Pig-1) of Drosophila melanogaster maps on the X chromosome, at polytene bands 3C11-12, and is nested within the 79 kb intron of the dunce gene. Pig-1 has so far been characterized only preliminarily and its function is still unknown. We analysed the molecular organization of the gene by cDNA clone isolation and sequencing as well as S1 mapping and primer extension analyses. The results obtained reveal that the gene is colinear with its genomic sequence and define the usage of both 5' and 3' alternative sites for Pig-1 transcription; two continuous open reading frames (ORFs) are fully contained within the Pig-1 transcribed region, although several lines of evidence suggest that only the longer ORF is likely to be translated. We also report that the level of Pig-1 transcript is nearly fourfold reduced in a variant strain carrying a deletion within the Pig-1 upstream sequence, thus identifying a regulatory element required for high level gene expression.

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