1.W.7. The (Bacillus Phage SPP1) Portal Protein 7 (PPP7) Family
The Bacillus phage SSP1 protein forms the portal vertex of the capsid (Lebedev et al. 2007). This portal plays critical roles in head assembly, genome packaging, neck/tail attachment, and genome ejection. The portal protein multimerizes as a single ring-shaped homododecamer arranged around a central channel. and binds to the terminase subunits to form the packaging machine. It is necessary to ensure correct procapsid size during capsid assembly. Once the capsid is packaged with the DNA, the terminase complex is substituted by the connector proteins gp15. DNA molecules of B. subtilis phage SPP1 exhibit terminal redundancy and are partially circularly permuted (Morelli et al. 1979).