Formation and Role of the Portal of Staphylococcus aureus Bacteriophage 80α

Bacteriophages play an important role in the pathogenicity of Staphylococcus aureus, an important human pathogen. Phages are involved in generalized and specialized transduction as well as a more specific process by which they mobilize elements known as phage-inducible chromosomal islands, of which S. aureus pathogenicity islands (SaPIs) are an important group. SaPIs are mobilized and packaged into virions made by structural proteins encoded by "helper" bacteriophages, such as 80α. The portal is a dodecameric ring located at a fivefold vertex of the phage capsid that serves multiple functions, including capsid assembly, DNA entry and exit, recruitment of ejection proteins, and tail attachment. We previously showed that portal protein expressed in E. coli forms tridecameric rings, while portals found in virions are always dodecamers. Here, we show that portals assembled at low temperature form unclosed rings that may represent portal assembly intermediates. By analyzing portal protein deletion mutants, we demonstrate the involvement of the different functional domains in phage assembly and protein incorporation.