THE PLANT CELL, Vol 4, Issue 9 1147-1156, Copyright © 1992 by American Society of Plant Biologists
The [beta] Subunit of Tomato Fruit Polygalacturonase Isoenzyme 1: Isolation, Characterization, and Identification of Unique Structural Features
L. Zheng, R. C. Heupel and D. DellaPenna
Department of Plant Sciences, Forbes Hall, University of Arizona, Tucson, Arizona 85721
We have purified and isolated cDNAs encoding the [beta] subunit of tomato
fruit polygalacturonase isoenzyme 1 (PG1), a cell wall protein that
associates with, and apparently regulates, the catalytic PG2 polypeptides.
Expression of the [beta] subunit is fruit specific and temporally separated
from the expression of PG2 during fruit development. The 37- to 39-kD
[beta] subunit is encoded as a 69-kD precursor protein containing a signal
sequence and two propeptide domains. The mature protein is composed almost
entirely of the novel 14-amino acid motif FTNYGxxGNGGxxx in which many of
the phenylalanine residues are post-translationally modified. The unique
structural features of the motif suggest an important role in the function
of the protein and hence in the activity of PG1. The [beta] subunit may
represent a class of bifunctional plant proteins that interact both with
structural components of the cell wall and catalytic proteins to localize
and/or regulate metabolic activities within the cell wall.
