In vitro synthesis and processing of a bean pathogenesis-related (PR4) protein

When bean plants (Phaseolus vulgaris var. Saxa) are treated with mercuric chloride or infected with alfalfa mosaic virus, they produce pathogenesis‐related (PR) proteins. We report here that functional mRNA encoding bean PR4 protein is only present when synthesis of this protein has been induced. Treatment with mercuric chloride results in a rapid induction of functional bean PR4 mRNA (within 2–3 h), whereas in virus‐infected plants this mRNA can only be detected the second day following the infection. Bean PR4 protein is synthesized in vitro, using this mRNA in a rabbit reticulocyte lysate system, as a precursor of 35 kDa. This precursor can be processed into a polypeptide having the same molecular mass (33.5 kDa) as the in vivo PR4 protein by the addition to the cell‐free translation system of canine pancreatic microsomal membranes.