Controllable molecular motors engineered from myosin and RNA.

Engineering biomolecular motors can provide direct tests of structure-function relationships and customized components for controlling molecular transport in artificial systems (1) or in living cells (2) . Previously, synthetic nucleic acid motors (3-5) and modified natural protein motors (6-10) have been developed in separate complementary strategies to achieve tunable and controllable motor function. Integrating protein and nucleic-acid components to form engineered nucleoprotein motors may enable additional sophisticated functionalities. However, this potential has only begun to be explored in pioneering work harnessing DNA scaffolds to dictate the spacing, number and composition of tethered protein motors (11-15) . Here, we describe myosin motors that incorporate RNA lever arms, forming hybrid assemblies in which conformational changes in the protein motor domain are amplified and redirected by nucleic acid structures. The RNA lever arm geometry determines the speed and direction of motor transport and can be dynamically controlled using programmed transitions in the lever arm structure (7,9) . We have characterized the hybrid motors using in vitro motility assays, single-molecule tracking, cryo-electron microscopy and structural probing (16) . Our designs include nucleoprotein motors that reversibly change direction in response to oligonucleotides that drive strand-displacement (17) reactions. In multimeric assemblies, the controllable motors walk processively along actin filaments at speeds of 10-20 nm s(-1). Finally, to illustrate the potential for multiplexed addressable control, we demonstrate sequence-specific responses of RNA variants to oligonucleotide signals.