Forms the portal vertex of the capsid (PubMed:17363899). 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. Binds to the terminase subunits to form the packaging machine. 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. Homododecamer (PubMed:8890151, PubMed:17363899). Has been seen as 13-mer and 14-mer multimer in experiments, but assembles as homododecamer in vivo (PubMed:8890151, PubMed:17363899). Interacts with the gp7 protein (PubMed:10656821, PubMed:12940981). Interacts with the connector proteins gp15; this interaction occurs at the end of the packaging when the terminase complex is replaced by the connector (PubMed:25991862). Belongs to the SPP1-like portal protein family.