A Drosophila SH2-SH3 Adaptor Protein Implicated in Coupling the Sevenless Tyrosine Kinase to an Activator of Ras Guanine Nucleotide Exchange, Sos

TLDR: Results suggest that drk binds autophosphorylated receptor tyrosine kinases with its SH2 domain and the Sos GNRP through its SH3 domains, thereby coupling receptor tyrose kinases to Ras activation.

About: This article is published in Cell.The article was published on 1993-04-09 and is currently open access. It has received 540 citations till now. The article focuses on the topics: SH3 domain & Receptor tyrosine kinase.

Figures

Figure 5. Binding of Wild-Type and Mutant Drk to Receptor Tyrosine Kinases

Figure 6. Localization of Wild-Type and Mutant Drk Protein in Eye Imaginal Discs Projections of optical sections of eye imaginal discs of wiid-type (A and C) and E(sev)2B mutant larvae (5 and D) stained with affinity-purified anti-drk antibodies are shown. Wild-type drk protein is highly concentrated at the apical membrane of all imaginal disc cells. In the morphogenetic furrow (black arrow in [A]) the density of ommatidial cells is higher, owing to their apical constriction in the furrow. Behind the morphogenetic furrow drk marks the assembly of the ommatidial clusters and is expressed at higher levels in a subpopulation of developing photoreceptor cells (C). The drkE(sev)2B protein, that carries a histidine to tyrosine amino acid substitution in the SH2 domain, is expressed at similar levels as the wild-type protein but is not associated with the cell membrane. Rather, it is localized in the cytoplasm. The black arrow head in (6) indicates the cytoplasmic drk staining in the flat cells of the peripodial membrane. Since drk is required for imaginal disc development, ommatidial assembly in E(sev)2B discs is abnormal. However, higher levels of mutant protein are still observed in cell clusters behind the morphogenetic furrow (white arrow in [B]). Scale bar, 10 μm.

Figure 8. A Model for the Role of Drk in Coupling-Activated Receptor Tyrosine Kinases to Sos

Figure 1. Sequence of Wild-Type and Mutant drk

Figure 7. Drk Binds to the Tail of Sos (A) The C-terminal tail of Sos contains potential SH3-binding sites. A sequence encompassing the Abl SH3-binding site in the protein 3BP-1 is compared with motifs in the C-terminal region of Sos. A proline-rich element, postulated to occupy the SH3 ligand-binding site. 1s boxed. Basic residues following the proline-rich elements of Sos are also outlined. (B) Bacterial lysates expressing GST, GST-Sos N, and GST-Sos tail were fractionated by SDS-PAGE and transferred to nitrocellulose. This filter was then incubated with purified bacterial drk protein. Binding of drk was detected by immunoblotting with anti-drk antibodies. An arrow indicates the mobility of the GST-Sos tail. (C) Protein lysates of torso-sev transgenic Drosophila, either uninduced (-) or heat shocked (+), were incubated with immobilized GST-Sos tail, and complexes were analyzed by immunoblotting with anti-drk antibodies. The position of drk is indicated.

Figure 3. Expression of the Drk Protein in Drosophila Tissues