Marino Zerial

Localization of rab Proteins

A number of in vitro and in vivo studies have shown that the large superfamily of Ras-related low molecular weight GTP-binding proteins includes proteins which are involved in the control of membrane traffic. In the yeast Saccharomyces cerevisiae, the SEC4 gene encodes a 23 Kd ras-related GTP-binding protein involved in the regulation of vesicular traffic from the Golgi apparatus to the plasma membrane. The protein is found associated with both the cytoplasmic surface of the plasma membrane and secretory vesicles (Salminen and Novick, 1987; Goud et al., 1988). Temperature-sensitive and dominant SEC4 mutants lead to a block in transport from the Golgi apparatus and accumulation of post-Golgi secretory vesicles (Salminen and Novick, 1987; Walworth et al., 1989). The YPT1 gene product is a 23 Kd GTP-binding protein (Gallwitz et al., 1983) which functions at an earlier step of the secretory pathway, from the ER to or within the Golgi apparatus (Schmitt et al., 1986; 1988; Segev and Botstein, 1987; Segev et al., 1988; Baker et al, 1990).