Biochemical analysis of torso and D-raf during Drosophila embryogenesis: implications for terminal signal transduction.
Determination of anterior and posterior terminal structures of Drosophila embryos requires activation of two genes encoding putative protein kinases, torso and D-raf. In this study, we demonstrate that Torso has intrinsic tyrosine kinase activity and show that it is transiently tyrosine phosphorylated (activated) at syncytial blastoderm stages. Torso proteins causing a gain-of-function phenotype are constitutively tyrosine phosphorylated, while Torso proteins causing a loss-of-function phenotype lack tyrosine kinase activity. The D-raf gene product, which is required for Torso function, is identified as a 90-kDa protein with intrinsic serine/threonine kinase activity. D-Raf is expressed throughout embryogenesis; however, the phosphorylation state of the protein changes during development. In wild-type embryos, D-Raf is hyperphosphorylated at 1 to 2 h after egg laying, and thereafter only the most highly phosphorylated form is detected. Embryos lacking Torso activity, however, show significant reductions in D-Raf protein expression rather than major alterations in the protein's phosphorylation state. This report provides the first biochemical analysis of the terminal signal transduction pathway in Drosophila embryos.
Sprenger
F
F
Max-Planck-Institut für Entwicklungsbiologie, Abteilung Genetik, Tübingen, Germany.
Trosclair
M M
MM
Morrison
D K
DK
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics*
D008024:Ligands; D004247:DNA; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases