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. 2006 Jan 23;34(2):606–612. doi: 10.1093/nar/gkj453

Figure 1.

Figure 1

Induction of cooperative and non-cooperative lac systems. (A) Relative β-galactosidase activities (corresponding to a plot of [Of]/[Ot]) of strain BMH 8117 (lacY−), harbouring a plasmid expressing wt Lac repressor and carrying on a λ prophage a lacZ gene driven by the wt lac promoter with all three operators, are plotted against the IPTG concentration in the growth medium. (B) Complex of wt Lac repressor with a DNA fragment carrying a single lac operator. The fraction ([Of]/[Ot]) of free DNA fragment (total fragment concentration is 5 × 10−11 M) in the presence of 2 × 10−10 M wt Lac repressor is plotted as a function of IPTG concentration. (C) As in (A), but in the presence of the first lac operator only. (D) As in (A), but harbouring a plasmid expressing dimeric active Lac repressor instead of wt tetrameric Lac repressor. To normalize the curves, values at 600 µM IPTG are set to 1.