Ariadne-1: A vital drosphila gene is required in development and defines anew conserved family of RING-finger proteins

We report the identification and functional characterization of ariadne-1 ( ari-1), a novel and vital Drosophila gene required for the correct differen tiation of most cell types in the adult organism. Also, we identify a seque nce-related gene, ari-2 and the corresponding mouse and human homologues of both genes. All these sequences define a new protein family by the Acid-ri ch, RING finger, B-box, RING finger, coiled-coil (ARBRCC) motif string. In Drosophila, ari-1 is expressed throughout development in all tissues. The m utant phenotypes are most noticeable in cells that undergo a large and rapi d membrane deposition, such as rewiring neurons during metamorphosis, large tubular muscles during adult myogenesis, and photoreceptors. Occasional su rvivors of null alleles exhibit reduced life span, motor impairments, and s hort and thin bristles. Single substitutions at key cysteines in each RING finger cause lethality with no survivors and a drastic reduction of rough e ndoplasmic reticulum that can be observed in the photoreceptors of mosaic e yes. In yeast two-hybrid assays, the protein ARI-1 interacts with a novel u biquitin-conjugating enzyme, UbcD10, whose sequence is also reported here. The N-terminal RING-finger motif is necessary and sufficient to mediate thi s interaction. Mouse and fly homologues of both ARI proteins and the Ubc ca n substitute for each other in the yeast two-hybrid assay, indicating that ARI represents a conserved novel mechanism in development. In addition to A RI homologues, the RBR signature is also found in the Parkinson-disease-rel ated protein Parkin adjacent to an ubiquitin-like domain, suggesting that t he study of this mechanism could be relevant for human pathology.