J. Biol. Chem., Vol. 263, Issue 2, 617-619, 01, 1988
Complete processing of a small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from pea requires the amino acid sequence Ile-Thr- Ser
CC Wasmann, B Reiss and HJ Bohnert
Department of Biochemistry, University of Arizona, Tucson 85721.
Chloroplast import and processing of two precursor proteins with mutations
in the carboxyl-terminal region of the transit peptide were examined in
vitro. Deletion mutations were introduced into the 57-amino acid transit
peptide of a chloroplast protein, the small subunit of
ribulose-1,5-bisphosphate carboxylase/oxygenase, from pea. A mutant,
PSd48/57, in which nine carboxyl-terminal amino acids of the transit
peptide had been deleted, was imported and processed to a series of 13- to
18-kDa polypeptides including the 14-kDa mature small subunit. In contrast,
processing of a mutant, PSd45/57, in which an additional three amino acids
had been removed, resulted in a series of polypeptides which did not
include the mature small subunit. Whereas PSd48/57 was imported as
efficiently as the wild-type precursor, import of PSd45/57 was only 25% as
efficient as that of the authentic precursor. The mutant precursor proteins
PSd48/57 and PSd45/57 are distinguished by a three-amino acid sequence,
Ile-Thr-Ser, located in the carboxyl-terminal region of the transit
peptide. We show that all or part of this sequence is required for correct
processing.
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