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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1972 May;69(5):1100–1103. doi: 10.1073/pnas.69.5.1100

Detection and Isolation of the Repressor Protein for the Tryptophan Operon of Escherichia coli

G Zubay *, Daniel E Morse , W Jurgen Schrenk ‡,§, J H M Miller ‡,
PMCID: PMC426639  PMID: 4338582

Abstract

DNA from a transducing bacteriophage carrying a fusion of the tryptophan and lactose operons of E. coli (λdtrp-lac) has been used to direct cell-free synthesis of β-galactosidase (EC 3.2.1.23). Whereas normal lac operon (λdlac) DNA requires adenosine-3′:5′-cyclic monophosphate (cAMP) for β-galactosidase synthesis, trp-lac DNA is unaffected by cAMP. This difference in cAMP dependence verifies the presence of a cAMP-requiring promoter in the lac operon that has been removed from the trp-lac DNA. Synthesis with trp-lac DNA is controlled by the protein product of the tryptophan repressor gene (trpR). Synthesis in extracts of trpR- (repressor-negative) cells is progressively reduced by increased additions of extract from trpR+ cells. No trpR- product repression is seen when β-galactosidase synthesis is programmed by normal lac DNA. This highly sensitive and specific assay has facilitated quantitation and partial purification of the trp repressor.

Keywords: β-galactosidase, transducing bacteriophage, cell-free extract, cyclic AMP, lac operon

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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