Single-molecule reconstitution of mRNA transport by a class V myosin

How a class V myosin transports mRNA is not well understood. Single-molecule reconstitution of messenger ribonucleoprotein complexes from purified proteins and a localizing mRNA in budding yeast demonstrates that the mRNA is instrumental in ensuring a stable, processive transport complex, whereas the number of localizing elements ('zip codes') influences run length and frequency. Molecular motors are instrumental in mRNA localization, which provides spatial and temporal control of protein expression and function. To obtain mechanistic insight into how a class V myosin transports mRNA, we performed single-molecule in vitro assays on messenger ribonucleoprotein (mRNP) complexes reconstituted from purified proteins and a localizing mRNA found in budding yeast. mRNA is required to form a stable, processive transport complex on actin—an elegant mechanism to ensure that only cargo-bound motors are motile. Increasing the number of localizing elements ('zip codes') on the mRNA, or configuring the track to resemble actin cables, enhanced run length and event frequency. In multi–zip-code mRNPs, motor separation distance varied during a run, thus showing the dynamic nature of the transport complex. Building the complexity of single-molecule in vitro assays is necessary to understand how these complexes function within cells.