The R ab GTP ase YPT ‐1 associates with G olgi cisternae and S pitzenkörper microvesicles in N eurospora crassa

Summary Vesicle traffic involves budding, transport, tethering and fusion of vesicles with acceptor membranes. GTP ‐bound small R ab GTP ases interact with the membrane of vesicles, promoting their association with other factors before their subsequent fusion. Filamentous fungi contain at their hyphal apex the S pitzenkörper ( S pk), a multivesicular structure to which vesicles concentrate before being redirected to specific cell sites. The regulatory mechanisms ensuring the directionality of the vesicles that travel to the S pk are still unknown. Hence, we analyzed YPT ‐1, the N eurospora crassa homologue of S accharomyces cerevisiae   Y pt1p ( R ab1), which regulates different secretory pathway events. Laser scanning confocal microscopy revealed fluorescently tagged YPT ‐1 at the S pk and putative G olgi cisternae. Co‐expression of YPT ‐1 and predicted post‐ G olgi R ab GTP ases showed YPT ‐1 confined to the S pk microvesicular core, while SEC ‐4 ( R ab8) and YPT ‐31 ( R ab11) occupied the S pk macrovesicular peripheral layer, suggesting that trafficking and organization of macro and microvesicles at the S pk are regulated by distinct R abs. Partial colocalization of YPT ‐1 with USO ‐1 (p115) and SEC ‐7 indicated the additional participation of YPT ‐1 at early and late G olgi trafficking steps.