Acetohydroxy acid synthase activity from a mutation at ilvF in Escherichia coli K-12.
Examination of the ilvF locus at 54 min on the Escherichia coli K-12 chromosome revealed that it is a cryptic gene for expression of a valine-resistant acetohydroxy acid synthase (acetolactate synthase; EC 4.1.3.18) distinct from previously reported isozymes. A spontaneous mutation, ilvF663, yielded IlvF+ enzyme activity that was multivalently repressed by all three branched-chain amino acids, was completely insensitive to feedback inhibition, was highly stable at elevated temperatures, and expressed optimal activity at 50 degrees C. The IlvF+ enzyme activity was expressed in strains in which isozyme II was inactive because of the ilvG frameshift in the wild-type strain K-12 and isozymes I and III were inactivated by point mutations or deletions. Tn5 insertional mutagenesis yielded two IlvF- mutants, with the insertion in ilvF663 in each case. These observations suggest that the ilvF663 locus may be a coding region for a unique acetohydroxy acid synthase activity.
Alexander-Caudle
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Department of Microbiology, Meharry Medical College, Nashville, Tennessee 37208.
Latinwo
L M
LM
Jackson
J H
JH
D000095:Acetolactate Synthase / Q000032:analysis* / Q000235:genetics; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007532:Isoleucine / Q000096:biosynthesis* / Q000235:genetics; D008970:Molecular Weight; D009154:Mutation; D007652:Oxo-Acid-Lyases / Q000032:analysis*; D014633:Valine / Q000096:biosynthesis* / Q000235:genetics
D007532:Isoleucine; D000095:Acetolactate Synthase; D007652:Oxo-Acid-Lyases; D014633:Valine