Diablo, a Kelch-like protein that interacts with the FH protein Diaphanous. K. Afshar 1, B. Stuart 2, S. Wasserman 1. 1) Ctr. Molecular Genetics, Univ. California at San Diego, La Jolla, CA; 2) UT Southwestern Medical Ctr. Dallas, TX.
Members of the Formin Homology (FH) family of proteins mediate cytokinesis as well as actin-mediated alterations in cell shape and polarity. Three conserved motifs are distributed along the amino acid sequence: an amino-terminal FH3 domain, a central proline-rich FH1 domain, and a carboxy-terminal FH2 domain flanked by coiled coils. The FH1 domain serves as a binding site for the actin-binding protein profilin, whereas the FH3 domain influences protein localization. Much less is known about the function of the most highly conserved sequence element, the FH2 domain. Drosophila encodes six FH proteins, one of which, Diaphanous, is required for cytokinesis. Using the yeast two-hybrid system we identified clones encoding Diablo, a protein that interacts with the FH2 domain of Diaphanous. Diablo is homologous to Kelch, containing both a BTB/POZ domain and six Kelch repeats. Deletion analysis reveals that it is the Kelch repeats that mediate specific interaction with the Diaphanous FH2 domain. Immunoprecipitation of Diaphanous from embryo extracts followed by immunoblotting with antibodies generated against Diablo reveals that the two proteins associate in vivo. In addition, Diablo expressed in ovaries from a heterologous promoter exhibits the same pattern of localization as Diaphanous. Based on these findings, we propose a role for the FH2 domain of Diaphanous in mediating organization of cortical actin structures.