First published online May 2, 2002; 10.1104/pp.001602
Plant Physiol, June 2002, Vol. 129, pp. 540-550
The Branched-Chain Amino Acid Transaminase Gene Family in
Arabidopsis Encodes Plastid and Mitochondrial
Proteins1
Ruth
Diebold,2
Joachim
Schuster,2
Klaus
Däschner, and
Stefan
Binder*
Molekulare Botanik, Universität Ulm, Albert-Einstein-Allee
11, 89069 Ulm, Germany
Branched-chain amino acid transaminases (BCATs) play a
crucial role in the metabolism of leucine, isoleucine, and valine. They
catalyze the last step of the synthesis and/or the initial step of the
degradation of this class of amino acids. In Arabidopsis, seven
putative BCAT genes are identified by their similarity to their
counterparts from other organisms. We have now cloned the respective
cDNA sequences of six of these genes. The deduced amino acid sequences
show between 47.5% and 84.1% identity to each other and about 30% to
the homologous enzymes from yeast (Saccharomyces cerevisiae) and mammals. In addition, many amino acids in
crucial positions as determined by crystallographic analyses of BCATs from Escherichia coli and human (Homo
sapiens) are conserved in the AtBCATs. Complementation of a
yeast  bat1/bat2 double knockout strain revealed that five AtBCATs
can function as BCATs in vivo. Transient expression of BCAT:green
fluorescent protein fusion proteins in tobacco (Nicotiana
tabacum) protoplasts shows that three isoenzymes are imported
into chloroplasts (AtBCAT-2, -3, and -5), whereas a single enzyme is
directed into mitochondria (AtBCAT-1).
1
This work was supported by the Fonds der
Chemischen Industrie and by the Anfangsförderung der
Universität Ulm. J.S. is a fellow of the Studienstiftung des
Deutschen Volkes.
2
These authors contributed equally to the paper.
*
Corresponding author; e-mail stefan.binder{at}biologie.uni-ulm.de;
fax 49-731-502-2626.
© 2002 American Society of Plant Physiologists
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