Identification and localization of gene expression of a low M(r) GTP-binding protein, ram p25 in pituitary gland

The localization of gene expression of a low M(r) GTP-binding protein, ram p25, was examined throughout the entire brain of adult rat by in situ hybridization. ram-mRNA was expressed predominantly in anterior and intermediate lobes of pituitary gland (hypophysis), and weakly in hippocampal formation. In other parts of brain, no significant expression of ram-mRNA was detected, indicating that ram p25 may have an important role(s) in adenohypophysis. In 15-day-fetal rat, the mRNA was observed to be expressed strongly in the primitive anterior lobe of pituitary gland. The ram p25 was also detected in bovine pituitary gland by a specific antibody and was purified to near homogeneity by stepwise column chromatographies. Biochemical characterization of the purified ram p25 revealed that the profile of [35S]GTP gamma S-binding activity was almost the same as that of recombinant ram p25 expressed in E. coli.