Significance of a common epitope of plant and animal endomembranes.

A rat monoclonal antibody that was raised against a common epitope on bean (Phaseolus vulgaris) endomembranes has been shown to cross-react with microsomal polypeptides from a number of plant and animal species. Immunoblotting has shown that the epitope is present on a large subset of polypeptides on microsomes of five animal species. The antigenic site appears to be accessible on intact bean membranes since it is readily digested by trypsin. The epitope is probably not derived post-translationally since the same Mr range is immunoprecipitated from polypeptides newly synthesized in vivo and in vitro. The polypeptides in bean appear to be regulated independently, one of Mr 58,000, in particular, was highly induced by treatment of suspension cultures with fungal elicitor. Preincubation of membranes enriched with endoplasmic reticulum and Golgi apparatus with the antibody blocks transfer of radioactivity from one compartment to the other in vitro. The common antigenic site could possibly be concerned in recognition or some fusion event during membrane trafficking within the cell.