title: Isolation of a mutant auxotrophic for L-alanine and identification of three major aminotransferases that synthesize L-alanine in Escherichia coli.
abstract: For Escherichia coli, it has been assumed that L-alanine is synthesized by alanine-valine transaminase (AvtA) in conjunction with an unknown alanine aminotransferase(s). We isolated alanine auxotrophs from a prototrophic double mutant deficient in AvtA and YfbQ, a novel alanine aminotransferase, by chemical mutagenesis. A shotgun cloning experiment identified two genes, uncharacterized yfdZ and serC, that complemented the alanine auxotrophy. When the yfdZ- or serC-mutation was introduced into the double mutant, one triple mutant (avtA yfbQ yfdZ) showed alanine auxotrophy, and another (avtA yfbQ serC), prototrophy. In addition, we found that four independent alanine auxotrophs possessed a point mutation in yfdZ but not in serC. We also found that yfdZ expression was induced in minimal medium. Furthermore, yfbQ-bearing plasmid conferred the ability to excrete alanine on the mutant lacking D-amino acid dehydrogenase-encoding gene, dadA. From these results, we concluded that E. coli synthesizes L-alanine by means of three aminotransferases, YfbQ, YfdZ, and AvtA.
authors: Laboratory of Animal Microbiology, Department of Microbial Biotechnology, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan. yoneyama@bios.tohoku.ac.jp
authors: Hiroshi
authors: H
authors: Yoneyama
authors: Hatsuhiro
authors: H
authors: Hori
authors: Sang-Jo
authors: SJ
authors: Lim
authors: Tatsuya
authors: T
authors: Murata
authors: Tasuke
authors: T
authors: Ando
authors: Emiko
authors: E
authors: Isogai
authors: Ryoichi
authors: R
authors: Katsumata