Regulation Mechanisms of the Synthesis of Pathogenesis-Related Proteins in Tobacco Leaves

Pathogenesis-related (PR) proteins, which are induced in responseto pathogenics and chemicals, were synthesized as larger precursorswith in vitro translation systems, and these precursors wereprocessed by dog pancreatic microsome membrane to become ofmature size. Two-dimensional gel electrophoresis showed thatat least six products were synthesized in vitro after immunoprecipitationwith an antibody against PR1a (most acidic PR protein). Thesefindings suggest the presence of at least six different kindsof precursors of the PR1 group (PR1), and also suggest the presenceof a microheterogenous multi-gene family which expresses PR1proteins in tobacco leaves. A comparison of the induction kineticsof mRNAs for PR1 proteins and the syntheses of these proteinsin vivo and in vitro showed the similarity of these processes,suggesting that the synthesis of PR1 proteins is regulated bya transcriptional step and occurs without delay by inductionof the production on of their mRNAs. A comparison between invitro and in vivo pulse labeling systems prepared from the sameleaves as to the incorporation efficiency of [35S]methionineinto PR1 proteins showed that the in vivo incorporation ratiowas at least 50 times higher than the in vitro one. However,for the incorporation of a small subunit of ribulose bisphosphatecarboxylase, as a control protein, the ratio was two to threetimes higher in the in vivo case. These findings indicate thatmRNAs for PR1 proteins are preferably translated to other normalproteins in chemically treated cells. (Received March 14, 1988; Accepted August 3, 1988)