We have isolated a cDNA clone, designated GTI, by screening a tobacco genetic tumor cDNA library with a tumor-specific “subtracted” cDNA probe. The cDNA contained the entire coding sequence for a 94-amino-acid polypeptide that exhibited significant homology to members of the proteinase inhibitor I family from tomato and potato. The predicted protein has a pre-sequence of 22 amino acids but lacks a pro-sequence, unlike genes for proteinase inhibitor I isolated to date. Furthermore, the protein encoded by GTI cDNA has a novel reactive site, having glutamine as the P 1 reactive residue. These results suggest that the GTI protein is a novel member of the proteinase inhibitor I family. The mRNA for GTI accumulated at a high level but only transiently after the wounding of tobacco plants. Thus, it appears that the GTI protein has a function that is related to the protection of tissues against damage due to wounding.
Copyright (C) 1993, The Japanese Society of Plant Physiologists
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