She2p, a novel RNA-binding protein tethers ASH1 mRNA to the Myo4p myosin motor via She3p

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Abstract
RNA localization is a widespread mechanism to achieve localized protein synthesis. In budding yeast, localization of ASH1 mRNA controls daughter cell‐specific accumulation of the transcriptional regulator Ash1p, which determines mating type switching. ASH1 mRNA localization depends on four independently acting sequences (‘zipcodes’) within the mRNA. In addition, the class V myosin Myo4p and a set of She proteins with as yet unknown function are essential for ASH1 localization. Here we show that She2p is a novel RNA‐binding protein that binds specifically to ASH1 mRNA in vivo and to ASH1 RNA zip codes in vitro . She2p can interact with She3 protein via She3p's C‐terminus and becomes localized to the daughter cell tip upon ASH1 expression. The N‐terminal coiled‐coil domain of She3p is required to form an RNA‐independent complex with the heavy chain of the myosin motor protein Myo4p. She2p and She3p are the first examples of adapters for tethering a localized mRNA to the motor protein and might serve as prototypes for RNA–motor protein adapters.