Interactions between coiled-coil proteins: Drosophila lamin Dm(0) binds tothe Bicaudal-D protein

in a yeast two-hybrid screen we identified an interaction between Drosophil a. lamin Dm(0), a structural nuclear protein, and BICD, a protein involved in oocyte development. The interaction can be reconstituted in vitro and ta kes place between segments of both proteins predicted to form coiled coils. The affinity for lamin Dm(0) of the minimal binding site on BICD is modula ted in a complex fashion by of her BICD segments. A point mutation, (FI)-I- 684, that causes the dominant, bicaudal, Bic-D phenotype inhibits lamin bin ding in the context of the minimal lamin-binding site, but not in a larger BICD fragment. The minimal lamin-binding site of BICD binds to a few other coiled-coil proteins, but binding to these proteins is not influenced by tb e (FI)-I-684 point mutation, suggesting that the interaction with lamin may play a role in Bic-D function. Our structural studies demonstrated that BI CD is 60-70% alpha-helical, is a dimer, and consists of two parts: a thin r od-shaped part of about 32 nm, and a thicker rod-shaped part of about 26 nm . Likely, the thinner rod-shaped part of fall-length BICD consists of the N -terminal half of the protein, and the lamin-binding site is located within the thicker rod shaped part.