PMID:14430363

Citation	PARDEE, AB and PRESTIDGE, LS (1959) On the nature of the repressor of beta-galactosidase synthesis in Escherichia coli.Biochim. Biophys. Acta 36:545-7
Abstract	No abstract in PubMed
Links	PubMed
Keywords	Escherichia coli; Glycoside Hydrolases
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Main Points of the Paper

• Hfr(z⁺i⁺) X F^-(z^-i^-):
  • within a few minutes of the time of entry of the z⁺i⁺ genes (which are closely linked) the synthesis of β-galactosidase commenced at maximal velocity in the absence of extracellular inducer
  • inducible i⁺ allele appears dominant over the constitutive i^- allele

• The idea that i⁺ could control the synthesis of a destructive enzyme which removes an endogenous intracellular inducer was eliminated due to observations from this paper (Figure 1, Curves C & D).

• The presence of 5-methyltryptophan enhances mating efficiency

• The data in this paper may suggest that:
  • an inducer-destroying enzyme is not responsible for the difference between inducibility and constitutivity
  • the repressor is not a protein, although the authors state this conclusion is open to doubt (evidence to refute this conclusion is shown here).

Materials and Methods Used

• Strains:
  • Hfr (z⁺i⁺)
  • F^- (z^-i^-)

• Conjugation

• Reagents
  • Streptomycin
  • Chloramphenicol
  • 5-methytryptophan
  • Duponol C(Na lauryl sulfate)

Phenotype Annotations

Species	Taxon ID	Strain	Gene (if known)	OMP	Phenotype	Details	Evidence	Notes
Escherichia coli	NCBI:562	lacZ- lacI-		Constitutive expression of beta-galactosidase	Expression	lac genes were transferred from Hfr (z+i+) into F- (z-i-) during conjugation and LacZ production became constitutive within the first few minutes after transfer	Biochemical Assay	Figure 1- curves A and B (LacZ assay)
Escherichia coli	NCBI:562	lacZ- lacI-		Inducible expression of beta-galactosidase (wt phenotype) Regulation of lacZ gene expression Repression of lacZ gene expression	Expression	lac genes were transferred from Hfr (z+i+) into F- (z-i-) during conjugation and LacZ production became inducible about an hour after transfer	Biochemical Assay	Figure 1- curve A vs. curve B (LacZ assay)
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