1.W.9.  The Escherichia coli Mu Phage Portal Protein 9 (PPP9) Family 

The phage Mu protein forms the portal vertex of the capsid (Grimaud 1996). 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 (Grimaud and Toussaint 1998). and binds to the terminase subunits to form the packaging machine. It also acts as a linker between the capsid and tail and is required for attachment of the neck proteins to the capsid. The viral genome is injected through the host cell envelope using a cntractile tail mechanism (Morgan et al. 2002).