CAP and RNA polymerase interactions with the lac promoter: Binding stoichiometry and long range effects

Michael G. Fried, Donald M. Crothers

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111 Scopus citations


The binding stoichiometries of the complexes formed when the E. coli cyclic AMP receptor protein (CAP) binds to 203 bp lac promoter-operator restriction fragments have been determined. Under quantitative binding conditions, a single dimer of CAP occupies each of two sites in the promoter. Different electrophoretic mobilities are observed for 1:1 complexes formed vrith L8-UV5 mutant, L305 mutant, and wild type promoter fragments, indicating sequence-specific structural differences between the complexes. The differences in gel mobility between L8-UV5 and wild type complexes disappear when the promoter fragments are cleaved with Hpa II restriction endonuclease. Models in which CAP alters DNA conformation or in which CAP forms a transient Intramolecular bridge between two domains of a DNA molecule could account for these observations. The selective binding of RNA polymerase to CAP-promoter complexes is demonstrated: the binding of a single CAP dimer to the promoter is sufficient to stimulate subsequent polymerase binding. Functional CAP molecules are not released from the promoter on polymerase binding.

Original languageEnglish
Pages (from-to)141-158
Number of pages18
JournalNucleic Acids Research
Issue number1
StatePublished - Jan 11 1983

Bibliographical note

Funding Information:
ACKNOWLEDGEMENTS This work was supported by grant PCM 75-17879 from Science Foundation, and by grant GM-21966 from the National Health.

ASJC Scopus subject areas

  • Genetics


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