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. 1989 Dec 20;8(13):4345–4350. doi: 10.1002/j.1460-2075.1989.tb08621.x

P22 repressor mutants deficient in co-operative binding and DNA loop formation.

D Valenzuela 1, M Ptashne 1
PMCID: PMC401647  PMID: 2531662

Abstract

We show here, both in vivo and in vitro, that P22 repressor binds co-operatively to operator sites separated by an integral number of turns of the DNA helix. We measure this co-operativity in vivo using an assay in which repression of a promoter requires co-operative binding of P22 repressors to two separated (non-adjacent) operator sites. We report the isolation of mutant repressors that have high affinity for single operator sites, but are defective in co-operative binding. Six different mutants, all bearing single amino acid changes in the carboxyl domain, have been isolated. We purified the two mutants most deficient in co-operative binding, and found that they bind non-co-operatively in vitro to adjacent as well as to non-adjacent pairs of operator sites.

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Selected References

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