Pathogenesis-related (PR) proteins, which are induced in response to pathogenics and chemicals, were synthesized as larger precursors with in vitro translation systems, and these precursors were processed by dog pancreatic microsome membrane to become of mature size. Two-dimensional gel electrophoresis showed that at least six products were synthesized in vitro after immunoprecipitation with an antibody against PR1a (most acidic PR protein). These findings suggest the presence of at least six different kinds of precursors of the PR1 group (PR1), and also suggest the presence of a microheterogenous multi-gene family which expresses PR1 proteins in tobacco leaves. A comparison of the induction kinetics of mRNAs for PR1 proteins and the syntheses of these proteins in vivo and in vitro showed the similarity of these processes, suggesting that the synthesis of PR1 proteins is regulated by a transcriptional step and occurs without delay by induction of the production on of their mRNAs. A comparison between in vitro and in vivo pulse labeling systems prepared from the same leaves as to the incorporation efficiency of [35S]methionine into PR1 proteins showed that the in vivo incorporation ratio was at least 50 times higher than the in vitro one. However, for the incorporation of a small subunit of ribulose bisphosphate carboxylase, as a control protein, the ratio was two to three times higher in the in vivo case. These findings indicate that mRNAs for PR1 proteins are preferably translated to other normal proteins in chemically treated cells.
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