DNA-binding properties of a lac repressor mutant incapable of forming tetramers

Michael D. Brenowitz, Nitai Mandal, Amy Pickar, Elizabeth Jamison, Sankar Adhya

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

The interaction of proteins bound to sites widely separated on the genome is a recurrent motif in both prokaryotic and eukaryotic regulatory systems. Lac repressor mediates the formation of "DNA loops" by the simultaneous interaction of a single protein tetramer with two DNA-binding sites. The DNA-binding properties of a Lac repressor mutant (LacIadi) deficient in the association of protein dimers to tetramers was investigated. The results of quantitative footprint and gel mobility-shift titrations suggest that the wild-type Lac represser (LacI+) binds cooperatively to two operator sites separated by 11 helical turns on a linear DNA restriction fragment by the formation of a "looped complex." LacIadi binds to this two-site operator non-cooperatively and without formation of a looped complex. These results demonstrate that the dimer-tetramer association of LacI+ is directly responsible for its cooperative binding and its ability to mediate formation of a looped complex. The Iadi mutation disrupts the monomer-dimer as well as eliminating the dimer-tetramer association equilibria while the DNA binding affinity of LacIadi to a single site is unchanged relative to the wild-type protein. These results suggest that DNA binding and dimer-tetramer association are functionally unlinked. The similarity of the DNA-binding properties of LacIadi and Gal repressor, a protein believed to function by mediating the formation of a looped complex, are discussed.

Original languageEnglish (US)
Pages (from-to)1281-1288
Number of pages8
JournalJournal of Biological Chemistry
Volume266
Issue number2
StatePublished - Jan 15 1991

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Lac Repressors
Dimers
DNA
Association reactions
Proteins
Titration
Genes
Monomers
Gels
Binding Sites
Genome
Mutation

ASJC Scopus subject areas

  • Biochemistry

Cite this

DNA-binding properties of a lac repressor mutant incapable of forming tetramers. / Brenowitz, Michael D.; Mandal, Nitai; Pickar, Amy; Jamison, Elizabeth; Adhya, Sankar.

In: Journal of Biological Chemistry, Vol. 266, No. 2, 15.01.1991, p. 1281-1288.

Research output: Contribution to journalArticle

Brenowitz, MD, Mandal, N, Pickar, A, Jamison, E & Adhya, S 1991, 'DNA-binding properties of a lac repressor mutant incapable of forming tetramers', Journal of Biological Chemistry, vol. 266, no. 2, pp. 1281-1288.
Brenowitz, Michael D. ; Mandal, Nitai ; Pickar, Amy ; Jamison, Elizabeth ; Adhya, Sankar. / DNA-binding properties of a lac repressor mutant incapable of forming tetramers. In: Journal of Biological Chemistry. 1991 ; Vol. 266, No. 2. pp. 1281-1288.
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