Figure 4.

mRNP transport complexes

A – ASH1 mRNA in yeast Saccharomyces cerevisiae. ASH1 is transported on F-actin cables, it is bound by RBP She2p co-transcriptionally, an adaptor She3p links RNA-She2p complex to a motor Myo4D in the cytoplasm [126]. B – RNA-stimulated assembly of transport complex for localized RNAs in Drosophila embryo. RBP Egalitarian (Egl) binds the RNA LE and promotes its interaction with the dimer of Bicaudal-D (BicD). RNA:Egl complex binding to BicD releases its autoinhibitory loop facilitating the interaction with dynein to form an active dynein-dynactin complex for the transport to the minus end of microtubules. Two Egl proteins are associated with one molecule of RNA [144]. C – Transport of septin mRNAs in fungus Ustilago maydis. mRNAs are bound by the RBP Rrm4 together with its partner Grp1 and transported on Rab5a positive early endosomes. The complex mRNA-Rrm4-Grp1, containing also Poly-A binding protein 1 (Pab 1), is tethered on endosomes through the adaptor Upa1. The mRNA is translated during the transport [184]. D – Model of β-catenin mRNA translational regulation. β-catenin mRNA accumulates in cytoplasmic translation factories, where it is translated and the newly-made β-catenin protein is degraded by the destruction complex. Upon WNT signalling activation, the factories are dissolved and the newly synthesized β-catenin migrates to the nucleus to activate transcription [31,192].