The Bacillus phage phi29 (φ29) portal protein of 309 aas.  It forms the portal vertex of the capsid (Ibarra et al. 2000; Fu and Prevelige 2009; Grimes et al. 2011). This portal plays 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.