Ypt11 Functions in Bud-Directed Transport of the Golgi by Linking Myo2 to the Coatomer Subunit Ret2

A yeast class V myosin Myo2 transports the Golgi into the bud during its inheritance. However, the mechanism that links the Golgi to Myo2 is unknown. Here, we report that Ypt11, a Rab GTPase that reportedly interacts with Myo2, binds to Ret2, a subunit of the coatomer complex. When Ypt11 is overproduced, Ret2 and the Golgi markers, Och1 and Sft2, are accumulated in the growing bud and are lost in the mother cell. In a ret2 mutant that produces the Ret2 protein with reduced affinity to Ypt11, no such accumulation is observed upon overproduction of Ypt11. At a certain stage of budding, it is known that the late Golgi cisternae labeled with Sec7-GFP show polarized distribution in the bud. We find that this polarization of late Golgi cisternae is not observed in the ypt11Delta mutant. Indeed, analyses of Sec7-GFP dynamics with spatio-temporal image correlation spectroscopy (STICS) and fluorescence loss in photobleaching (FLIP) reveals that Ypt11 is required for the vectorial actin-dependent movement of the late Golgi from the mother cell toward the emerging bud. These results indicate that the Ypt11 and Ret2 are components of a Myo2 receptor complex that functions during the Golgi inheritance into the growing bud.