The Drosophila melanogaster flightless-I gene involved in gastrulation and muscle degeneration encodes gelsolin-like and leucine-rich repeat domains and is conserved in Caenorhabditis elegans and humans.

Mutations at the flightless-I locus (fliI) of Drosophila melanogaster cause flightlessness or, when severe, incomplete cellularization during early embryogenesis, with subsequent abnormalities in mesoderm invagination and in gastrulation. After chromosome walking, deficiency mapping, and transgenic analysis, we have isolated and characterized flightless-I cDNAs, enabling prediction of the complete amino acid sequence of the 1256-residue protein. Data base searches revealed a homologous gene in Caenorhabditis elegans, and we have isolated and characterized corresponding cDNAs. By using the polymerase chain reaction with nested sets of degenerate oligonucleotide primers based on conserved regions of the C. elegans and D. melanogaster proteins, we have cloned a homologous human cDNA. The predicted C. elegans and human proteins are, respectively, 49% and 58% identical to the D. melanogaster protein. The predicted proteins have significant sequence similarity to the actin-binding protein gelsolin and related proteins and, in addition, have an N-terminal domain consisting of a repetitive amphipathic leucine-rich motif. This repeat is found in D. melanogaster, Saccharomyces cerevisiae, and mammalian proteins known to be involved in cell adhesion and in binding to other proteins. The structure of the maternally expressed flightless-I protein suggests that it may play a key role in embryonic cellularization by interacting with both the cytoskeleton and other cellular components. The presence of a highly conserved homologue in nematodes, flies, and humans is indicative of a fundamental role for this protein in many metazoans.

The sluggish-A gene of Drosophila melanogaster is expressed in the nervous system and encodes proline oxidase, a mitochondrial enzyme involved in glutamate biosynthesis.

Certain gene mutations in Drosophila melanogaster cause sluggish motor activity. We have localized the transcription unit of the sluggish-A gene to a 14.7-kb region at the base of the X chromosome and have cloned corresponding cDNAs. The predicted protein product has significant sequence similarity to Saccharomyces cerevisiae proline oxidase (EC 1.5.99.8), a mitochondrial enzyme which catalyzes the first step in the conversion of proline to glutamate. In the mutant fly, mitochondrial proline oxidase activity is reduced and has kinetic properties different from those of the wild type, providing further evidence that the gene encodes proline oxidase. Indeed, the free proline level in mutant flies is elevated. When the mutant is rescued by transformation, the proline oxidase and free proline levels, as well as the motor and phototactic behavior, are restored to normal. During embryonic development the sluggish-A transcript is predominantly expressed in the nervous system. Significantly, it has previously been reported that a mouse mutant, PRO/Re, which has reduced proline oxidase activity and elevated free proline levels, also exhibits sluggish behavior.

Chromosome structure at interfaces between major chromatin types: alpha- and beta-heterochromatin.

The chromocenter of Drosophila polytene chromosomes, which consists of two major chromatin types, has long been a troublesome region in molecular terms. The recent microcloning of part of this region, the isolation of a monoclonal antibody to a beta-heterochromatin binding protein, and new in situ studies now shed a little more light on this chromosomal region.