A plasmid (pI-14), containing part of the phage λ control region (EcoRI-D fragment of λ cJ857) with a large deletion between genes rex and kil, confers a cold-sensitive (cs) phenotype on the host bacteria, whereas the parent plasmid (pMM200) without the deletion made the host bacteria (Escherichia coli strain DOO) high-temperature sensitive. This phenomenon could be explained on the basis of the sequence analysis of the deletion. Upon this deletion, the λ kil gene, which was originally under the control of the pLpromoter, was brought under the control of the λ cI promoters, resulting in the reversal of the host cell response to temperature. This example shows that gene circuits showing diametrically opposite responses to environmental factors (in this case, temperature) can be constructed from the same elements when the effector gene (here, kil) is connected in different ways to the sensor gene (here, cI857). This cold-dependent killing activity was also dependent on the crp+state of the host. © 1994.
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