title: Interactions of the Escherichia coli methionine repressor with the metF operator and with its corepressor, S-adenosylmethionine.
abstract: The metJ gene encoding the methionine aporepressor was placed under the control of a strong and inducible promoter, ptac. Bacterial strains carrying the recombinant plasmid pIP35 overproduced the regulatory protein by a factor of 200 over the wild type strain as determined by the immunoblot technique. The purified metJ gene product negatively controls the expression of the metF gene, in a cell-free system as shown by repression of beta-galactosidase synthesis under the control of the metF promoter. The metJ protein binds to a DNA fragment containing the potential operator of the metF gene with an affinity which is 10 times greater in the presence of S-adenosylmethionine than in its absence. Equilibrium dialysis experiments showed that the met aporepressor binds 2 mol of S-adenosylmethionine per mol of dimer with a dissociation constant of 200 microM.
mesh_terms: D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005796:Genes; D005798:Genes, Bacterial; D005809:Genes, Regulator; D008715:Methionine / Q000235:genetics*; D009693:Nucleic Acid Hybridization; D010957:Plasmids; D012097:Repressor Proteins / Q000235:genetics* / Q000302:isolation & purification; D012436:S-Adenosylmethionine / Q000494:pharmacology*; D014157:Transcription Factors / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D012097:Repressor Proteins; D014157:Transcription Factors; D012436:S-Adenosylmethionine; D008715:Methionine; D001616:beta-Galactosidase