Identification of the <i>Lymantria dispar</i> Nucleopolyhedrovirus Envelope Fusion Protein Provides Evidence for a Phylogenetic Division of the <i>Baculoviridae</i>

<jats:title>ABSTRACT</jats:title> <jats:p> The complete genome sequences of a number of diverse members of the <jats:italic>Baculoviridae</jats:italic> including both nucleopolyhedroviruses (NPVs) and granuloviruses (GVs) revealed that they lack a homolog of GP64, the envelope fusion protein of the budded form of <jats:italic>Autographa californica</jats:italic> multinucleocapsid NPV (Ac <jats:italic>M</jats:italic> NPV) and its close relatives. Computer-assisted analyses of the genome of one of these viruses, <jats:italic>Lymantria dispar M</jats:italic> NPV (Ld <jats:italic>M</jats:italic> NPV), revealed a single open reading frame ( <jats:italic>ld130</jats:italic> ) whose product had the predicted properties of a membrane protein. Characterization of the localization of the products of the full-length <jats:italic>ld130</jats:italic> gene and of an <jats:italic>ld130</jats:italic> -enhanced green fluorescent protein gene ( <jats:italic>egfp</jats:italic> ) fusion using both immunofluorescence and fluorescence microscopy revealed that LD130 accumulates at the plasma membranes of cells infected with Ld <jats:italic>M</jats:italic> NPV or transfected with <jats:italic>ld130-egfp</jats:italic> . In addition, cells transfected with either <jats:italic>ld130</jats:italic> or <jats:italic>ld130-egfp</jats:italic> or infected with wild-type virus undergo membrane fusion at pH 5. Western blot analyses indicate that LD130 is present in infected cells as an 83-kDa protein and is also present in budded virions as a protein doublet containing bands of 81 and 83 kDa. Tunicamycin treatment of infected cells resulted in an immunoreactive band of about 72 kDa, indicating that LD130 is N-glycosylated. Whereas the distribution of <jats:italic>gp64</jats:italic> appears to be confined to a relatively closely related group of NPVs, homologs of <jats:italic>ld130</jats:italic> are present in a diverse number of both NPVs and GVs. This suggests that LD130 may be the primordial baculovirus envelope fusion protein. </jats:p>