Identification of Six Autographa californica Multicapsid Nucleopolyhedrovirus Early Genes That Mediate Nuclear Localization of G-Actin

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Abstract
Nuclear filamentous actin (F-actin) is required for nucleopolyhedrovirus (NPV) progeny production in NPV-infected, cultured lepidopteran cells. We have determined that monomeric G-actin is localized within the nuclei of host cells during the early stage of infection by Autographa californica multicapsid nucleopolyhedrovirus (Ac M NPV). With a library of cloned Ac M NPV genomic fragments, along with a plasmid engineered to express enhanced green fluorescent protein- Bombyx mori G-actin in transient transfection experiments, we identified six Ac M NPV early genes that mediate nuclear localization of G-actin in TN-368 cells: ie-1 , pe38 , he65 , Ac004, Ac102, and Ac152 . Within this subset, ie-1 and pe38 encode immediate-early transcriptional transactivators, he65 encodes a delayed-early product, and the products encoded by Ac004, Ac102, and Ac152 have not been characterized. We found that when driven by foreign promoters, ie-1 , pe38, and Ac004 had to be expressed prior to Ac102 or he65 for nuclear G-actin to accumulate and that expression of Ac152 was no longer required. These results and others suggested that the product of Ac152 was a transactivator (directly or indirectly) of both Ac102 and he65 and that recruitment of G-actin to the nucleus was a temporally regulated process. Determining the functions of each of the six Ac M NPV gene products with respect to our assay should provide valuable clues to basic cellular mechanisms of actin regulation and how Ac M NPV infection affects them.