Genes encoding for branched-chain amino acid aminotransferase are differentially expressed in plants

The final metabolic step in the production of the amino acids leucine, isol eucine and valine is a transamination reaction catalyzed by the enzyme bran ched-chain amino acid aminotransferase (BCAT). Using complementation of an Escherichia coli ilvE mutant we have isolated two different cDNAs from pota to (Solanum tuberosum) encoding for BCAT (BCAT1 and BCAT2). BCAT1 and BCAT2 were 86 % identical to each other based on deduced amino acid sequence. So uthern analysis indicated that BCAT1 and BCAT2 are not in identical regions of the genome and that BCAT1 may exist in multiple copies. The deduced ami no acid sequences for both cDNAs contained putative transit peptides for pl astid or mitochondrial localization demonstrating spatial expression of the gene products. Northern analysis showed an induction of BCAT1, relative to BCAT2, in leaf tissues exposed to proliferative hormone treatments suggest ing that a response to increased growth, and the deed for branched-chain am ino acid metabolism associated with that growth, is limited to the expressi on of BCAT1. (C) 2001 Editions scientifiques et medicales Elsevier SAS.