The pKO2 Linear Plasmid Prophage ofKlebsiella oxytoca

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Abstract
Temperate bacteriophages with plasmid prophages are uncommon in nature, and of these only phages N15 and PY54 are known to have a linear plasmid prophage with closed hairpin telomeres. We report here the complete nucleotide sequence of the 51,601-bpKlebsiella oxytocalinear plasmid pKO2, and we demonstrate experimentally that it is also a prophage. We call this bacteriophage φKO2. An analysis of the 64 predicted φKO2 genes indicate that it is a fairly close relative of phage N15; they share a mosaic relationship that is typical of different members of double-stranded DNA tailed-phage groups. Although the head, tail shaft, and lysis genes are not recognizably homologous between these phages, other genes such as the plasmid partitioning, replicase, prophage repressor, and protelomerase genes (and their putative targets) are so similar that we predict that they must have nearly identical DNA binding specificities. The φKO2 virion is unusual in that its phage λ-like tails have an exceptionally long (3,433 amino acids) central tip tail fiber protein. The φKO2 genome also carries putative homologues of bacterialdinIandumuDgenes, both of which are involved in the host SOS response. We show that these divergently transcribed genes are regulated by LexA protein binding to a single target site that overlaps both promoters.