Evidence that repression mechanisms can exert control over the thr, leu, and ilv operons of Escherichia coli K-12.
Mutants of Escherichia coli K-12 resistant to either the threonine analog DL-alpha-amino-beta-hydroxyvaleric acid or the leucine analog 5',5',5'-trifluoro-DL-leucine were isolated. One DL-alpha-amino-beta-hydroxyvaleric acid-resistant mutant strain, designated SP572, constitutively expressed the thr and ilv operons. The mutant allele, avr-16, was localized between trpR and the thr operon at min 0. The wildtype allele of avr-16, designated ileR, is trans dominant. One 5',5',5'-trifluoro-DL-leucine-resistant mutant strain, designated FLR9, expressed the leu and ilv operons constitutively. The mutant allele, flr-9, is linked to entA at min 13. The constitutive expression of the thr, leu, and ilv operons in mutants avr-16 and flr-9 was partly reversed in cells harboring a plasmid, which leads to elevated levels of the trpR gene product, the Trp aporepressor protein. Operator-like sequences situated upstream from the transcription startpoints of the thr, leu, and ilv operons are plausible candidates for targets of systems of repressor-operator control functioning in parallel with attenuation.
D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D005838:Genotype; D007532:Isoleucine / Q000235:genetics*; D007930:Leucine / Q000031:analogs & derivatives* / Q000235:genetics* / Q000633:toxicity; D009154:Mutation; D009876:Operon / Q000187:drug effects; D013045:Species Specificity; D013912:Threonine / Q000235:genetics*; D014633:Valine / Q000235:genetics*
D007532:Isoleucine; D013912:Threonine; C035177:5',5',5'-trifluoroleucine; D007930:Leucine; D014633:Valine