ASSOCIATION OF RAP1A AND RAP1B PROTEINS WITH LATE ENDOCYTIC PHAGOCYTIC COMPARTMENTS AND RAP2A WITH THE GOLGI-COMPLEX/

Among the small GTPases of the Ras family, Rap proteins exhibit the hi ghest homology with p21Ras. The four Rap proteins so far identified co nstitute two subgroups, comprising the Rap1(A,B) and the Rap2(A,B) pro teins. The intracellular location of Rap1A, Rap1B and Rap2A proteins w as investigated in mammalian cells by confocal immunofluorescence micr oscopy. Using a specific anti-Rap1 affinity-purified antibody, both Ra p1A and Rap1B proteins were localized to late endocytic compartments ( late endosomes/lysosomes) in fibroblasts. The localization of the Rap1 A and B proteins transiently overexpressed with the vaccinia T7 system was identical to that observed for endogenous Rap1 proteins. In contr ast, epitope-tagged Rap2A protein colocalized with several markers of the Golgi complex, thus indicating that its site of function was disti nct from that of Rap1A. In addition, morphological and subcellular fra ctionation studies provided evidence for the association of Rap1 prote ins with phagosomes displaying biochemical features of late endocytic structures in J774 macrophages. Thus, the localization of Rap1A and Ra p1B implicates their involvement in late endocytic/phagocytic processe s.