RESEARCH ARTICLE Invertebrate and Vertebrate Class III Myosins Interact with MORN Repeat- Containing Adaptor Proteins

In Drosophila photoreceptors, the NINAC-encoded myosin III is found in a complex with a small, MORN-repeat containing, protein Retinophilin (RTP). Expression of these two pro-teins in other cell types showed NINACmyosin III behavior is altered by RTP. NINAC dele-tion constructs were used to map the RTP binding site within the proximal tail domain of NINAC. In vertebrates, the RTP ortholog is MORN4. Co-precipitation experiments demon-strated that human MORN4 binds to human myosin IIIA (MYO3A). In COS7 cells, MORN4 and MYO3A, but not MORN4 and MYO3B, co-localize to actin rich filopodia extensions. De-letion analysis mapped the MORN4 binding to the proximal region of the MYO3A tail do-main. MYO3A dependent MORN4 tip localization suggests that MYO3A functions as a motor that transports MORN4 to the filopodia tips and MORN4 may enhance MYO3A tip lo-calization by tethering it to the plasma membrane at the protrusion tips. These results estab-lish conserved features of the RTP/MORN4 family: they bind within the tail domain of myosin IIIs to control their behavior