Repression of the E. coli lactose operon by cooperation between two individually unproductive "half-operator" sites.
Two remote and weak lac regressor binding sites can be used jointly to repress the synthesis of beta-galactosidase in E. coli, while they cannot separately. When this result is discussed in reference to the various modes of cooperation between the sites, it supports with a new approach a model implying the simultaneous binding of lac repressor to both sites with the formation of a DNA loop. In connection with this point, we present a new strategy to detect cooperative interactions in vivo, based on the asymmetry of the DNA binding site, formally equivalent here to a half-site, heterodimerization of the protein, and influence of orientation of the sites on repression at short and long distance.
Amouyal
M
M
Département de Biologie Moléculaire, Institut Pasteur, Paris.
von Wilcken-Bergmann
B
B
D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D015870:Gene Expression / Q000235:genetics; D005827:Genetics, Microbial; D007763:Lac Operon / Q000235:genetics*; D009875:Operator Regions, Genetic / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics; D001616:beta-Galactosidase / Q000235:genetics
D004269:DNA, Bacterial; D014157:Transcription Factors; D001616:beta-Galactosidase