Ag. Smith et al., ISOLATION OF A CDNA-ENCODING CHLOROPLAST FERROCHELATASE FROM ARABIDOPSIS-THALIANA BY FUNCTIONAL COMPLEMENTATION OF A YEAST MUTANT, The Journal of biological chemistry, 269(18), 1994, pp. 13405-13413
Ferrochelatase catalyzes the insertion of ferrous iron into protoporph
yrin IX to form protoheme. It is located in the mitochondria in all eu
karyotes and is also found in plastids in plants. Although it has been
purified from animals and microorganisms, and genes for it isolated a
nd characterized, very little is known about plant ferrochelatases. We
have isolated a cDNA for ferrochelatase from the higher plant Arabido
psis thaliana by functional complementation of a mutant of Saccharomyc
es cerevisiae defective in this enzyme. The cDNA encodes a protein of
52 kDa, which has 25-35% sequence similarity to ferrochelatases from o
ther organisms. There is an N-terminal extension of about 65 residues,
which is almost certainly the chloroplast transit peptide, since the
precursor protein, transcribed and translated in vitro, is efficiently
imported and processed to the mature size by isolated pea chloroplast
s. In contrast, the precursor was not processed by mitochondrial proce
ssing peptidase activity, nor could import into isolated yeast mitocho
ndria be demonstrated conclusively, although, presumably, in the rescu
ed yeast mutant, at least some of the Arabidopsis ferrochelatase must
be present in the mitochondria. A single transcript the same size as t
he cDNA was detected in both Arabidopsis leaves and roots, although th
e amount of message was greater in the photosynthetic tissue. Southern
analysis suggests that there is a single gene for chloroplast ferroch
elatase in Arabidopsis.