Rab 11a is modifiedin vivoby isoprenoid geranylgeranyl

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Abstract
Post‐translational adduction of farnesyl or geranylgeranyl moieties to a terminal cysteine residue of proteins is a characteristic feature ofras‐related GTP‐binding proteins. According to current rules of prenylation the carboxylterminal motif (CXXX or CC/CXC) as well the context of the cysteine residue dictate the extend and specificity of the isoprenoid modification. Rab 11a, a small GTP‐binding protein that is associated with pathways regulating protein traffic, terminates with isoleucine at itsC‐terminus, suggesting that it may only be geranylgeranylated. Recent finding, however, showed that rab 11a can be modifiedin vitroby different prenyl groups: farnesyl and geranylgeranyl [1]. To determine whether rab 11a is modifiedin vivoby both isoprenoids we transiently overexpressed rab 11a in COS1 cells, and analyzed the translation products by two‐dimensional polyacrylamide gel electrophoresis (2‐D PAGE) in combination with metabolic labeling in the presence of either [3H]farnesyl‐PP or [3H]geranylgeranyl‐PP. Contrary to thein vitroresults, our studies showed that rab 11a is post‐translationally modifiedin vivoonly by geranylgeranyl isoprenoid. The data implied thatin vivothere must exist other determinant(s) that are necessary for prenyltransferase recognition.