THE PLANT CELL, Vol 1, Issue 5 559-566, Copyright © 1989 by American Society of Plant Biologists
Maturation and Subcellular Compartmentation of Potato Starch Phosphorylase
N. Brisson, H. Giroux, M. Zollinger, A. Camirand and C. Simard
Department of Biochemistry, University of Montreal, P.O. Box 6128, Station A, Montreal, Quebec H3C 3J7, Canada
The subcellular localization and maturation of starch phosphorylase (EC
2.4.1.1) was studied in developing potato tubers. The enzyme is localized
inside the stroma of amyloplasts in young tubers, whereas in mature tubers
it is found within the cytoplasm in the immediate vicinity of the plastids.
A phosphorylase cDNA clone was isolated and used in RNA gel blot
experiments to demonstrate that phosphorylase mRNAs are of the same size
and abundance in both young and mature tubers. In vitro translation of
mRNAs followed by immunoprecipitation with a phosphorylase antiserum
indicates that the enzyme is synthesized as a higher molecular weight
precursor in both young and mature tubers. The presence of a transit
peptide at the N terminus of the protein was confirmed by the sequencing of
the phosphorylase cDNA clone. The transit peptide has several structural
features common to transit peptides of chloroplast proteins but contains a
surprisingly large number of histidine residues. The mature form of the
enzyme is present in both young and mature tubers, suggesting that a
similar processing of the transit peptide may take place in two different
subcellular locations.
