Affiliation:
1. Applied Molecular Microbiology, Division of Applied Life Sciences, Graduate School of Agriculture,1 and
2. Applied Molecular Microbiology, Division of Integrated Life Science, Graduate School of Biostudies,2 Kyoto University, Kyoto, Japan
Abstract
ABSTRACT
Tyrosine phenol-lyase (Tpl), which can synthesize 3,4-dihydroxyphenylalanine from pyruvate, ammonia, and catechol, is a tyrosine-inducible enzyme. Previous studies demonstrated that the
tpl
promoter of
Erwinia herbicola
is activated by the TyrR protein of
Escherichia coli
. In an attempt to create a high-Tpl-expressing strain, we cloned the
tyrR
gene of
E. herbicola
and then randomly mutagenized it. Mutant TyrR proteins with enhanced ability to activate
tpl
were screened for by use of the
lac
reporter system in
E. coli
. The most increased transcription of
tpl
was observed for the strain with the mutant
tyrR
allele involving amino acid substitutions of alanine, cysteine, and glycine for valine-67, tyrosine-72, and glutamate-201, respectively. A
tyrR
-deficient derivative of
E. herbicola
was constructed and transformed with a plasmid carrying the mutant
tyrR
allele (V67A Y72C E201G substitutions). The resultant strain expressed Tpl without the addition of tyrosine to the medium and produced as much of it as was produced by the wild-type strain grown under tyrosine-induced conditions. The regulatory properties of the mutant TyrR
V67A
, TyrR
Y72C
, TyrR
E201G
, and TyrR
V67A Y72C E201G
proteins were examined in vivo. Interestingly, as opposed to the wild-type TyrR protein, the mutant TyrR
V67A
protein had a repressive effect on the
tyrP
promoter in the presence of phenylalanine as the coeffector.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
43 articles.
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