During intracellular proliferation, the phages of this family produce empty icosahedral capsids (proheads or procapsids) and tails.
The λ-like phages are a family of tailed, dsDNA bacteriophages. The critical role of TerS in the Rpp–TerS complex is to escort TerL to the PICI cosN, ensuring appropriate DNA cutting and packaging. We propose that the Rpp–TerS complex binds to a site in the island DNA that is positioned analogous to that of the phage DNA but has a completely different sequence. Our communication reviews published data about the hijacking mechanism and its implications for phage DNA packaging. The Rpp–TerS interaction prevents phage DNA packaging while sponsoring PICI DNA packaging. This is achieved by an island-encoded protein (Rpp) that binds to the phage protein (TerS), which normally selects phage DNA for packaging from a DNA pool that includes the helper phage and host DNAs. In the case of recently described Gram-negative PICIs, the PICI changes the specificity of DNA packaging. The hijacking strategy includes preventing the helper phage from packaging its own DNA while enabling PICI DNA packaging. Rather, PICIs hijack virion assembly functions from an induced prophage acting as a helper phage. PICIs lack a complete set of morphogenetic genes needed to construct mature virus particles. Recent work by the Penadés laboratory elucidates how a helper phage infection or prophage induction induces the island to excise from the bacterial chromosome, replicate, and become packaged into functional virions.
PICIs have acquired genes that alter the genetic repertoire of the bacterial host, including supplying virulence factors.
The phage-inducible chromosomal islands (PICIs) of Gram-negative bacteria are analogous to defective prophages that have lost the ability to propagate without the aid of a helper phage.
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