Ash1p is a transcriptional repressor necessary for mating-type switching in budding yeast, and its messenger RNA is transported into the bud where the protein is ultimately needed. To get there, the mRNA rides into the bud along actin tracks, carried by the myosin V-type motor Myo4p. But how does the RNA hang on to the motor? Ralf-Peter Jansen and colleagues now report in the EMBO Journal that they have found the missing link.

Genetic screens had determined that She2p and She3p are involved in ASH1 mRNA localization ? but what exactly do they do? Jansen and colleagues found, through a biochemical approach, that She2p is the long-sought-after RNA-binding protein, specific for ASH1 mRNA. Furthermore, they showed that She3p is an adaptor that binds She2p through its carboxyl terminus and Myo4p through its amino terminus. Whereas She3p is associated with this myosin motor constitutively, and can be transported into the bud even in the absence of ASH1 mRNA, She2p needs to bind ASH1 mRNA to interact efficiently with She3p.

So it seems that the transport of ASH1 mRNA is pretty much solved. But how many other mRNAs might be localized in yeast, and should we expect similar chains of linkers for each of them?