The Drosophila gene abstrakt, required for visual system development, encodes a putative RNA helicase of the DEAD box protein family

The molecular mechanisms underlying axonal pathfinding are not well underst ood. In a genetic screen for mutations affecting the projection of the larv al optic nerve we isolated the abstrakt locus. abstrakt is required for pat hfinding of the larval optic nerve, and it also affects development in both the adult visual system and the embryonic CNS. Here we report the molecula r characterization of abstrakt. It encodes a putative ATP-dependent RNA hel icase of the DEAD box protein family, with two rare substitutions in the PT RELA and the RG-D motifs, thought to be involved in oligonucleotide binding : serine for threonine, and lysine for arginine, respectively. Two mutant a lleles of abstrakt show amino acid exchanges in highly conserved positions. A glycine to serine exchange in the HRIGR motif, which is involved in RNA binding and ATP hydrolysis, results in a complete loss of protein function; and a proline to leucine exchange located between the highly conserved ATP ase A and PTRELA motifs results in temperature-sensitive protein function. Both the broad requirement for abstrakt gene function and its ubiquitous ex pression are consistent with a molecular function of the abstrakt protein i n mRNA splicing or translational control. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.