Structure of the bacteriophage 80α neck shows the interactions between DNA, tail completion protein and tape measure protein.

Tailed bacteriophages with double-stranded DNA genomes (class ) play an important role in the evolution of bacterial pathogenicity, both as carriers of genes encoding virulence factors and as the main means of horizontal transfer of mobile genetic elements (MGEs) in many bacteria, such as . The pathogenicity islands (SaPIs), including SaPI1, are a type of MGEs are that carry a variable complement of genes encoding virulence factors. SaPI1 is mobilized at high frequency by "helper" bacteriophages, such as 80α, leading to packaging of the SaPI1 genome into virions made from structural proteins supplied by the helper.

Structure of the Portal Complex from Staphylococcus aureus Pathogenicity Island 1 Transducing Particles In Situ and In Isolation.

Staphylococcus aureus is an important human pathogen, and the prevalence of antibiotic resistance is a major public health concern. The evolution of pathogenicity and resistance in S. aureus often involves acquisition of mobile genetic elements (MGEs).

Structure of the portal complex from pathogenicity island 1 transducing particles in situ and in solution.

is an important human pathogen, and the prevalence of antibiotic resistance is a major public health concern. The evolution of pathogenicity and resistance in often involves acquisition of mobile genetic elements (MGEs). Bacteriophages play an especially important role, since transduction represents the main mechanism for horizontal gene transfer.

Competing scaffolding proteins determine capsid size during mobilization of pathogenicity islands.

pathogenicity islands (SaPIs), such as SaPI1, exploit specific helper bacteriophages, like 80α, for their high frequency mobilization, a process termed 'molecular piracy'. SaPI1 redirects the helper's assembly pathway to form small capsids that can only accommodate the smaller SaPI1 genome, but not a complete phage genome. SaPI1 encodes two proteins, CpmA and CpmB, that are responsible for this size redirection.

Derepression of SaPIbov1 Is Independent of φNM1 Type 2 dUTPase Activity and Is Inhibited by dUTP and dUMP.

Staphylococcus aureus is an opportunistic human pathogen able to transfer virulence genes to other cells through the mobilization of S. aureus pathogenicity islands (SaPIs). SaPIs are derepressed and packaged into phage-like transducing particles by helper phages like 80α or φNM1.