| The interaction of FGF 1 and GRP75 / mortalin in vivo was confirmed by co immunoprecipitation , immunohistochemical co localization in Rat 1 fibroblasts and by using the yeast two hybrid system . ^^^ Moreover , a binding assay in vitro with the use of recombinant FGF 1 and mortalin demonstrated a direct physical interaction between the two proteins . ^^^ These results reveal that GRP75 / mortalin is an intracellular FGF 1 binding protein in cells and suggest that GRP75 / mortalin is involved in the trafficking of and / or signalling by FGF 1 . . ^^^ |