ABSTRACT
One of the first RAS-related proteins to be identified and purified was a 22-kDa protein, designated Gp (also later called G25K). Initial isolation was based on the ability of the protein to bind radiolabeled guanine nucleotides and utilized a detergent extract of a human placental particulate fraction as a source. 1 Subsequently, the same or very similar protein was identified and purified from detergent extracts of human platelet 2 and bovine brain membranes. 3 Primary amino acid sequence obtained from peptide fragments derived from both the human placental and platelet preparations demonstrated the existence of highly conserved regions implicated in GTP-binding/GTP hydrolysis and allowed for the generation of highly specific antipeptide sera. 4 The availability of primary sequence also allowed for the cloning of the cDNA’s encoding this RAS-related protein. 5 , 6 Here we will focus on recent studies suggesting a link between this protein and signaling pathways activated by receptor tyrosine kinases and also the information currently available on the protein-protein interactions that serve to regulate their GDP-binding/GTPase cycle.
