Autographa californica multiple nucleopolyhedrovirus Ac51 interacts with Ac66 and facilitates its nuclear localization to promote the nuclear egress of nucleocapsids

Autographa californica multiple nucleopolyhedrovirus is a large DNA virus that replicates within host nuclei. The mechanism underlying the nuclear egress of viral nucleocapsids is not fully understood. We previously identified Ac51 as a key player in facilitating efficient nuclear egress of nucleocapsids for the release of budded viruses (BVs). This protein joins Ac66 and EXON0 as the third identified protein with a similar function. In this study, we evaluated the functional importance of conserved domains of Ac51 during virus replication and found that the coiled-coil (CC) motif of Ac51 was crucial for the protein's accumulation and BV production. Our study further revealed a strong interaction and colocalization between Ac51 and Ac66. Deletion of <i>ac51</i> significantly impaired the nuclear import of Ac66, leading to its aggregation in the cytoplasm. Deletion of the CC motif also significantly reduced the nuclear localization of Ac66 and their colocalization, while deletion of the DnaJ domain of Ac51 seemed to impair the interaction between Ac51 and Ac66 <i>in vitro</i>. Molecular docking analysis provided a potential interaction mechanism between Ac51 and Ac66. Intriguingly, our study also identified two other viral nucleocapsid proteins, ME53 and Ac132, which interacted and colocalized with both Ac51 and Ac66. Molecular docking analysis suggested distinct binding regions of ME53 and Ac132 within the Ac51-Ac66 complex. In summary, these results demonstrated that Ac51 and Ac66 cooperate to facilitate the nuclear egress of nucleocapsids and uncovered a functional correlation between ME53/Ac132 and the Ac51-Ac66 complex in nucleocapsid assembly or transport.IMPORTANCEThe nuclear egress of AcMNPV nucleocapsids is a crucial step for producing high levels of budded viruses, but its underlying mechanism is not fully understood. Previous studies have highlighted the significant roles of three nucleocapsid proteins, including Ac51, Ac66, and EXON0, in facilitating efficient nuclear egress of nucleocapsids. Here, we demonstrated a strong interaction and colocalization between Ac51 and Ac66, but not between Ac51 and EXON0. Furthermore, Ac51 is required for efficient nuclear localization of Ac66, indicating that Ac51 exerts a role in Ac66 to promote nucleocapsid egress. Our study also identified two other nucleocapsid proteins, ME53 and Ac132, which interacted and colocalized with both Ac51 and Ac66, suggesting their functional correlation in nucleocapsid assembly or transport. These discoveries enhanced our understanding of the functional mechanism of Ac51 and nucleocapsid assembly and transport and provided insights for further investigation of the nucleocapsid transport process.