Characterization and nucleotide sequence of a colicin-release gene in the hic region of plasmid ColE3-CA38.

Downstream from its colicin and immunity genes (col. imm), Escherichia coli plasmid ColE3-CA38 contains a 0.81-kb DNA segment, the hic region, which is required for high colicin production. Characterization of derived plasmids, carrying the col-imm operon but varying in the hic region, showed that the latter functions in lacuna production, colicin release, cell death, and lysis. The hic gene expression after induction was shown to be dependent on the col gene promoter. The nucleotide sequence of the 0.81-kb region was determined and the hic gene localized to its imm-distal portion following an open reading frame (ORF) with no known function. There are two overlapping ORFs in that portion of the sequence, one of which was identified as the hic gene by its partial homology to lysis gene H of CloDF13. The 3' half of the hic gene is non-essential and contains a terminator-like DNA sequence. Preceding the gene, there are also inverted repeats which may attenuate its transcription.