1.W.6. The (Bacillus Phage phi29) Portal Protein 6 (PPP6) Family
The phage phi29 portal protein forms the portal vertex of the capsid (Ibarra et al. 2000; Fu and Prevelige 2009; Grimes et al. 2011).
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 (Guasch et al. 2002; Grimes et al. 2011). It binds to the 6 packaging RNA molecules (pRNA) forming a double-ring
structure which in turn binds to the ATPase gp16 hexamer, forming the
active DNA-translocating motor (Xiao et al. 2005; Simpson et al. 2000). This complex is essential for the specificity of packaging from the left DNA end. Thus, it is involved in viral genome ejection through the host cell envelope and penetration into the host cytoplasm.