Fig. 6: Symmetry mismatches and AcMNPV cccDNA packaging mechanism.

A Schematic representation of the AcMNPV apical cap showing the anchoring of the C21 portal vertex onto the various assemblies forming the rest of the mature virion apex. The C21 ring contains Ac66 N-termini while Ac66 residues 310–386 are visible on the C14 anchor-1 ring bound to PTP. Ac101 also participate in the C21 ring through their N-termini whereas Ac101 residues 112-219 are part of both the C14 anchor-2 ring and the C2 plug. The different complexes are color coded according to Fig. 1, see legend on the right. B Proposed AcMNPV genome packaging mechanism. I: Preassembled nucleocapsid with overall C7 apical cap recruits newly amplified covalently closed circular DNA (cccDNA) genome decorated with Ac54 and other unknown subunits of the packaging motor (e.g. GTA). II: Genome docking triggers the C7 plug to adopt a C2 symmetry probably mediated by Ac54 and Ac101/Ac144 dimer. III: Full packaging apparatus assembles and genome translocation, involving putative helical-to-planar mechanism and ASCE P-Loop ATPase, is favored by symmetry mismatch at the interface between the motor and the rest of the nucleocapsid (C21 vs. C2). IV: Complete genome packaging ends up with packaging of cccDNA closure loop and partial dissociation of the translocating motor as probably being dependent on DNA presence and thus allowing for its recycling. Maintained symmetry mismatch between C14 anchor complexes and C2 plug, in mature virion, may favor later apical capsid dissociation for pressurized DNA release in infected cells.