Abstract
Understanding where in the cytoplasm mRNAs are translated is increasingly recognized as being as important as knowing the timing and level of protein expression. mRNAs are localized via active motor-driven transport along microtubules (MTs) but the underlying essential factors and dynamic interactions are largely unknown. Using biochemical in vitro reconstitutions with purified mammalian proteins, multicolor TIRF-microscopy, and interaction kinetics measurements, we show that adenomatous polyposis coli (APC) enables kinesin-1- and kinesin-2-based mRNA transport, and that APC is an ideal adaptor for long-range mRNA transport as it forms highly stable complexes with 3'UTR fragments of several neuronal mRNAs (APC-RNPs). The kinesin-1 KIF5A binds and transports several neuronal mRNP components such as FMRP, PURα and mRNA fragments weakly, whereas the transport frequency of the mRNA fragments is significantly increased by APC. APC-RNP-motor complexes can assemble on MTs, generating highly processive mRNA transport events. We further find that end-binding protein 1 (EB1) recruits APC-RNPs to dynamically growing MT ends and APC-RNPs track shrinking MTs, producing MT minus-end-directed RNA motility due to the high dwell times of APC on MTs. Our findings establish APC as a versatile mRNA-kinesin adaptor and a key factor for the assembly and bidirectional movement of neuronal transport mRNPs.