FUNCTIONALITY AND SPECIFIC MEMBRANE LOCALIZATION OF TRANSPORT GTPASESCARRYING C-TERMINAL MEMBRANE ANCHORS OF SYNAPTOBREVIN-LIKE PROTEINS

Ras-related guanine nucleotide-binding proteins of the Ypt/Rab family fulfill a pivotal role in vesicular protein transport both in yeast an d in mammalian cells. Proper functioning of these proteins involves th eir cycling between a GTP- and a GDP-bound state as well as their reve rsible association with specific membranes. Here we show that the yeas t Ypt1 and Sec4 proteins, essential components of the vesicular transp ort machinery, allow unimpaired vesicular transport when permanently f ixed to membranes by membrane-spanning domains replacing their two C-t erminal cysteine residues. Membrane detachment of the GTPases therefor e is not obligatory for transport vesicle docking to or fusion with an acceptor membrane. It was also found that the membrane anchors derive d from different synaptobrevin-related proteins have targeting informa tion and direct the chimeric GTPases to different cellular compartment s, presumably from the endoplasmic reticulum via the secretory pathway .