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. 2016 Jul 4;44(14):6625–6638. doi: 10.1093/nar/gkw600

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© The Author(s) 2016. Published by Oxford University Press on behalf of Nucleic Acids Research.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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Figure 4. — Assay of roadblocking by λ CI and Cro. Roadblock readthrough is defined as the LacZ activity obtained in the presence of the DNA-binding protein, which binds a site between the promoter and the LacZ reporter, divided by the LacZ activity obtained in the absence of the DNA-binding protein. Means and 95% confidence limits of the ratios are shown. (A) The interaction between LacI and its operator Oid presents a strong roadblock to transcription. LacI was supplied from pUHA-1, with pUHA-1ΔlacI used for the no protein control (n = 4). (B–E) Wild-type λ CI or DNA-binding enhanced CI mutants, CI(E83K) or CI(G48S) (45), were supplied by IPTG induction (100 μM) of pZE15cI/cI(E83K)/cI(G48S) (n = 6) (these reporter strains also carried pUHA1 for LacI-mediated control of CI expression). (F) λ Cro binding to OR is also a weak roadblock to transcription. λ Cro was similarly supplied by pZE15cro, with pZE15 serving as the no protein control (n = 9).