mRNA and ER transport in yeast

As a first and comparably simple model, we analyze the directional transport of ASH1 mRNA in the budding yeast S. cerevisiae. Besides mRNA, this cargo-transport complex consists of the myosin motor Myo4p, its bound adapter She3p, and the RNA-cargo binding protein She2p.

We began our studies by determining the X-ray structures of the cargo-binding protein She2p (Niessing et al. 2004). Although dimeric in the crystal structure, She2p is a functional tetramer in solution (Müller et al. 2009).
We also characterized the binding of the myosin motor Myo4p to its cargo adapter She3p. In contrast to its vertebrate homologs, the type V myosin motor Myo4p is strictly monomeric (Heuck et al. 2007). Structure determination of the Myo4p globular tail revealed strong similarity to membrane-tethering complexes (Heuck et al. 2010), suggesting a role of this domain not only in cargo binding, but also in mRNP anchoring.
More recently, we showed that She3p is a previously uncharacterized RNA binding protein that acts synergistically with She2p for the specific recognition of localizing mRNAs (Müller et al. 2011). Since this synergistic complex only assembles in the cytoplasm, selection of mRNAs for localization may be limited to the late cytoplasmic step of mature complex assembly.