Yeast Ran-binding protein 1 (Yrb1) shuttles between the nucleus and cytoplasm and is exported from the nucleus via a CRM1 (XPO1)-dependent pathway

The RanGTP-binding protein RanBP1, which is located in the cytoplasm, has b een implicated in release of nuclear export complexes from the cytoplasmic side of the nuclear pore complex. Here we show that Yrb1 (the yeast homolog of RanBP1) shuttles between the nucleus and the cytoplasm. Nuclear import of Yrb1 is a facilitated process that requires a short basic sequence uithi n the Ran-binding domain (RBD). By contrast, nuclear export of Yrb1 require s an intact RBD, which forms a ternary complex wvith the Xpo1 (Crm1) NES re ceptor in the presence of RanGTP. Nuclear export of Yrb1, however, is insen sitive towards leptomycin B, suggesting a novel type of substrate recogniti on between Yrb1 and Xpo1. Taken together, these data suggest that ongoing n uclear impart and export is an important feature of Yrb1 function in vivo.