Affiliation:
1. International Institute of Genetics and Biophysics, C. N. R., 80125 Naples, Italy
Abstract
Three mutations (
ilvH611, ilvH612
, and
ilvH613
) are described which make
Escherichia coli
K-12 resistant to valine inhibition and are located near
leu
. The expression of the
ilv
genes appears to be normal in these mutants since the isoleucine-valine biosynthetic enzymes are not derepressed relative to the wild type. The intracellular concentration of valine is, however, higher in the mutants than in the isogenic
ilvH
+
strain. These mutants also excrete valine, probably because of the high intracellular concentration of this amino acid. The pool size of valine is regulated independently from that of isoleucine and leucine. The increased intracellular concentration of valine is due to a decreased feedback inhibition that valine exerts on its own biosynthetic pathway. In fact, acetolactate synthase activity assayed in extracts of
ilvH612
and
ilvH613
mutants is more resistant to valine inhibition than the activity assayed in the
ilvH
+
isogenic strain. Two forms of acetolactate synthase activity can be separated from these extracts by adsorption and elution on hydroxylapatite. One of them is as sensitive to valine inhibition as that of the wild type, the other is more resistant to valine inhibition.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
24 articles.
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