Specificity domains distinguish the Ras-related GTPases Ypt1 and Sec4.
The essential Ras-related GTPases Ypt1 and Sec4 act at distinct stages of the secretion pathway in the yeast Saccharomyces cerevisiae: Ypt1 is required for vesicular transport from the endoplasmic reticulum to the Golgi apparatus, whereas Sec4 is required for fusion of secretory vesicles to the plasma membrane. Here we use chimaeras of the two proteins to identify a 9-residue segment of Ypt1 that, when substituted for the analogous segment of Sec4, allows the chimaera to perform the minimal functions of both proteins in vivo. This segment corresponds to loop L7 of the p21ras crystal structure. Substitution of a 24-residue Ypt1 segment, including the residues just mentioned, together with 12 residues of Ypt1 corresponding to the 'effector region' of p21ras (loop L2; refs 7,8), transforms Sec4 into a fully functional Ypt1 protein without residual Sec4 function.
Dunn
B
B
Department of Genetics, Stanford University School of Medicine, California 94305.
Stearns
T
T
Botstein
D
D
D000595:Amino Acid Sequence; D003460:Crystallization; D005656:Fungal Proteins / Q000737:chemistry; D019204:GTP-Binding Proteins / Q000737:chemistry*; D006026:Glycoside Hydrolases / Q000378:metabolism; D006031:Glycosylation; D008969:Molecular Sequence Data; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D043324:beta-Fructofuranosidase; D020691:rab GTP-Binding Proteins
D005656:Fungal Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase; D019204:GTP-Binding Proteins; C060755:YPT1 protein, S cerevisiae; C064320:SEC4 protein, S cerevisiae; D016283:Proto-Oncogene Proteins p21(ras); D020691:rab GTP-Binding Proteins