P22 repressor mutants deficient in co-operative binding and DNA loop formation.
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.
Valenzuela
D
D
Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, MA 02138.
Ptashne
M
M
D010582:Bacteriophage lambda / Q000235:genetics; D001483:Base Sequence; D004279:DNA, Viral / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D012475:Salmonella / Q000235:genetics*; D012483:Salmonella Phages / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics
D004279:DNA, Viral; D012097:Repressor Proteins; D014157:Transcription Factors; D001616:beta-Galactosidase