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Catabolite-Insensitive Revertants of Lac Promoter Mutants

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The maximum rate of expression of the lac operon is severely reduced in lac promoter mutants. Revertants of these mutations which produce higher levels of enzyme were isolated. Some of these revertants had lost sensitivity to catabolite repression and transient repression. The mutations responsible for these losses took place at sites very close to the original promoter mutations. From these results we conclude that the promoter itself is the target site for both catabolite and transient repression of the lac operon.
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... The constitutive 'native' phage promoter pA was replaced with the placUV5 promoter, generating the pPop-upLac series of the single-plasmid nanorod production vectors ( Figures S5 and S7). The placUV5 promoter is insensitive to catabolic repression by glucose (Silverstone et al. 1970), hence the nanorod production is inducible even in the presence of glucose in the medium. The inducible-replication plasmid (named pPop-up529LacUni) carried the same BSFpn cassette [529 nt, containing (−) ori, and producing 80-nm nanorods] as the original constitutive-pIIexpression pPop-up plasmid (pPop-up529Uni). ...
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