COLD-SENSITIVE PHENOTYPE OF ESCHERICHIA-COLI-CELLS HARBORING A PLASMID CARRYING THE KIL GENE OF PHAGE-LAMBDA BROUGHT UNDER CONTROL OF CI857GENE PROMOTERS

A plasmid (pI-14), containing part of the phage lambda control region (EcoRI-D fragment of lambda c1857) with a large deletion between genes rex and kil, confers a cold-sensitive (cs) phenotype on the host bact eria, whereas the parent plasmid (pMM200) without the deletion made th e host bacteria (Escherichia coli strain DOO) high-temperature sensiti ve. This phenomenon could be explained on the basis of the sequence an alysis of the deletion. Upon this deletion, the lambda kil gene, which was originally under the control of the p(L) promoter, was brought un der the control of the lambda 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 fa ctors (in this case, temperature) can be constructed from the same ele ments when the effector gene (here, kil) is connected in different way s to the sensor gene (here, c1857). This cold-dependent killing activi ty was also dependent on the crp(+) state of the host.