A direct interaction between the RNA-binding proteins Staufen and Tm1-I/C in the oskar mRNA transport complex

In the Drosophila female germline, oskar messenger RNA is transported on microtubules from the nurse cells to the posterior pole of the oocyte, where it is translated. Transport of oskar transcripts from the nurse cells into the oocyte requires dynein, while localization of the mRNAs within the oocyte to the posterior pole is dependent upon kinesin-1. Staufen, a double-stranded RNA (dsRNA)-binding protein, has been shown to bind the oskar mRNA transport complex in the oocyte and inactivate dynein; however, it remains unclear how kinesin is activated. Here, using surface plasmon resonance, nuclear magnetic resonance spectroscopy, and RNA imaging within egg chambers, we demonstrate that Staufen directly interacts with Tropomyosin1-I/C (Tm1), a non-canonical kinesin adaptor. This work provides molecular evidence of how Staufen integrates into the oskar messenger ribonucleoprotein (mRNP) complex.