Regulation of gene expression in plasmid ColE1: delayed expression of the kil gene.

cea, imm, and kil are a cluster of three functionally related genes of the plasmid ColE1. The cea and kil genes are in the same inducible operon, with transcription being initiated from a promoter adjacent to the cea gene. The imm gene is located between the cea and kil genes, but it is transcribed in the opposite direction. Complementary interaction between the imm mRNA and the anti-imm sequences in the middle of the cea-kil transcript causes a pronounced delay in expression of the kil gene when the cea-kil operon is induced. A segment in the overlapping region between the cea and imm genes causes delayed expression of the kil gene in the absence of imm gene transcription. This delay effect increases the yields of colicin synthesized in induced cells.