Assembly of the arc repressor-operator complex: cooperative interactions between DNA-bound dimers
1993; American Chemical Society; Volume: 32; Issue: 5 Linguagem: Inglês
10.1021/bi00056a022
ISSN1943-295X
AutoresBronwen M. Brown, Robert T. Sauer,
Tópico(s)Metal complexes synthesis and properties
ResumoArc repressor, a member of the beta-ribbon family of DNA binding proteins, binds to its 21-base-pair operator as a tetramer. Here, the Arc dimer is shown to bind specifically to DNA fragments containing operator half-sites, and the equilibrium and kinetic constants for these reactions are determined. DNA-bound dimers are also shown to be transient intermediates in association experiments, indicating that assembly of the Arc tetramer-operator complex occurs by sequential addition of dimers to operator half-sites. When the left or right operator half-site is occupied by an Arc dimer, cooperative interactions increase the affinity of the second dimer by approximately 5900-fold [delta delta G = -5.1 (+/- 0.5) kcal/mol]. This increase in affinity is largely caused by an increase in the half-life of the complex; "non-cooperatively" bound dimers dissociate with a half-life of a few seconds while "cooperatively" bound dimers have half-lives of more than 1 h.
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