Volume 272, Number 47, Issue of November 21, 1997 pp. 29430-29433
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

COMMUNICATION:
A 50-Picosiemens Anion Channel of the Chloroplast Envelope Is Involved in Chloroplast Protein Import

(Received for publication, August 6, 1997, and in revised form, October 1, 1997)

From the Department of Plant Physiology, Wageningen Agricultural University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands

Single channel recordings were used to investigate the changes on the pea chloroplast envelope during protein import. In the inside-out patch configuration a 50-picosiemens (pS) anion channel of the chloroplast envelope membrane was identified. The open time probability of the channel was decreased by the addition of the wild type precursor protein of ferredoxin (wt-prefd) to the pipette-filling solution in the presence of 0.5 mM ATP. In the absence of ATP or in the presence of 50 µM ATP, wt-prefd did not affect the open time probability of the channel. A deletion mutant of prefd, 6-14-prefd, which is inactive in in vitro import, was also unable to affect the open time probability of the 50-pS anion channel. In the presence of 100 µM ATP, wt-prefd decreased the open time probability of the channel to a lesser extent, as did the transit peptide alone. It is concluded that the 50-pS anion channel could be part of the protein import machinery of the inner membrane. In addition the precursor protein under import conditions induced burst-like increases of the envelope conductivity. The implication of both responses for the chloroplast protein import process are discussed.

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