PLANT PHYSIOLOGY , Vol 106, Issue 2 771-777, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Posttranslational Modification of an Isoinhibitor from the Potato Proteinase Inhibitor II Gene Family in Transgenic Tobacco Yields a Peptide with Homology to Potato Chymotrypsin Inhibitor I
M. T. McManus, W. A. Laing, J. T. Christeller and DWR. White
Plant Molecular Genetics Laboratory, Grasslands Research Centre, AgResearch, Private Bag 11008, Palmerston North, New Zealand (M.T.M., D.W.R.W.)
A member of the potato proteinase inhibitor II (PPI-II) gene family under
the control of the cauliflower mosaic virus 35S promoter has been
introduced into tobacco (Nicotiana tabacum). Purification of the PPI-II
protein that accumulates in transgenic tobacco has confirmed that the
N-terminal signal sequence is removed and that the inhibitor accumulates as
a protein of the expected size (21 kD). However, a smaller peptide of
approximately 5.4 kD has also been identified as a foreign gene product in
transgenic tobacco plants. This peptide is recognized by an anti-PPI-II
antibody, inhibits the serine proteinase chymotrypsin, and is not observed
in nontransgenic tobacco. Furthermore, amino acid sequencing demonstrates
that the peptide is identical to a lower molecular weight chymotrypsin
inhibitor found in potato tubers and designated as potato chymotrypsin
inhibitor I (PCI-I). Together, these data confirm that, as postulated to
occur in potato, PCI-I does arise from the full-length PPI-II protein by
posttranslational processing. The use of transgenic tobacco represents an
ideal system with which to determine the precise mechanism by which this
protein modification occurs.
