PLANT PHYSIOLOGY , Vol 113, Issue 2 479-485, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
A 28-Kilodalton Pod Storage Protein of French Bean Plants (Purification, Characterization, and Primary Structure)
P. Y. Zhong, T. Tanaka, D. Yamauchi and T. Minamikawa
Department of Biology, Tokyo Metropolitan University, Minami-ohsawa 1-1, Hachioji, Tokyo 192-03, Japan
When French bean (Phaseolus vulgaris) plants were depodded in the early
stages of fruit development, relative levels of a specific protein with a
relative molecular weight of 28,000 were enhanced in the young pods that
formed later. The protein, designated pod storage protein (PSP), was
purified from extracts of newly formed pods from plants that had been
previously depodded four times at intervals of 2 weeks. Two-dimensional
polyacrylamide gel electrophoresis showed the presence of three forms
(designated A, B, and C) of PSP with identical electrophoretic mobilities
but different charges. The molecular mass of native PSP was estimated by
gel filtration to be 67 kD; therefore, the protein was most likely present
as a dimer. The antisera raised against forms A and C were cross-reactive
with each other. Form B lacked the N-terminal alanine of forms A and C. An
expression library from French bean pods was screened using the antiserum
against form A, and a full-length cDNA clone was isolated. The cDNA insert
included 765 bp potentially encoding a polypeptide with 255 amino acid
residues (and a calculated molecular mass of 28,854 D). The amino acid
sequence deduced from the PSP cDNA had 65 to 71% identity with soybean
(Glycine max) vegetative storage protein sequences (P.E. Staswick [1988]
Plant Physiol 87: 250-254; and Correction [1989] Plant Physiol 89: 717).
Genomic Southern blot analysis suggested that PSP is derived from a
single-copy gene.
