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P22 repressor mutants deficient in co‐operative binding and DNA loop formation.
Author(s) -
Valenzuela D.,
Ptashne M.
Publication year - 1989
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1989.tb08621.x
Subject(s) - repressor , biology , mutant , dna , operator (biology) , psychological repression , microbiology and biotechnology , genetics , gene , transcription factor , gene expression
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.