THE PLANT CELL, Vol 1, Issue 5 551-557, Copyright © 1989 by American Society of Plant Biologists
The 18-kD Protein That Binds to the Chloroplast DNA Replicative Origin Is an Iron-Sulfur Protein Related to a Subunit of NADH Dehydrogenase
M. Wu, Z. Q. Nie and J. Yang
Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, Maryland 21228
From a high-salt extract of the purified thylakoid membrane, an 18-kD
protein was detected. This protein was translated by the chloroplast
ribosomes and could form a stable DNA-protein complex with a cloned
chloroplast DNA replicative origin [Nie, Z.Q., Chang, D.Y., and Wu, M.
(1987) Mol. Gen. Genet. 209, 265-269]. In this paper, the 18-kD protein is
linked to frxB, a chloroplast-encoded, ferredoxin-type, iron-sulfur
protein, by N-terminal microsequencing of the purified protein and computer
analysis. The identification is further supported empirically by the fact
that the electron paramagnetic resonance spectra of the protein indicate
the presence of iron-sulfur clusters. A polyclonal antibody raised against
a synthetic pentadecameric peptide with amino acid sequence corresponds to
the highly conserved region of the frxB protein and reacts strongly and
specifically with the 18-kD protein band in protein gel blot analyses. The
18-kD iron-sulfur protein is found to be related to a subunit of the
respiratory chain NADH dehydrogenase by its cross-reaction with a
polyclonal antibody raised against highly purified NADH-ubiquinone
oxidoreductase, a key enzyme of the respiratory chain. These data are
consistent with chlororespiration, and, thus, possible implication of
chlororespiration in regulating the initiation of chloroplast DNA
replication is discussed.
