Characteristics of the transactivator gene ie1 of Spodoptera exigua multiple nucleopolyhedrovirus

The genomic position and nucleotide sequence of the immediate early gene ie l of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) were determin ed. The SeMNPV iel gene had the potential to encode a protein of 714 amino acids with a predicted molecular mass of 82.0 kDa, representing the largest baculovirus IE1 known to date. The similarity of SeMNPV IE1 with IE1 prote ins from other baculoviruses was restricted to the basic C-terminal two-thi rds of the protein, which is involved in DNA binding. A single iel transcri pt of 2.5 kb was detected at 1 h p.i., peaking at 8 h p.i. and disappearing at 24 h p.i. From 8 h p.i. onwards a 1.7 kb transcript was detected, which became more abundant late in infection. Primer extension analysis revealed the use of several start sites early and late in infection. One of these w as located in the promoter motif CAGT located at position -15 relative to t he translational start codon, most intensively used at 8 h p.i. Four kb ups tream of the SeMNPV iel gene, ORF xd244 was identified with homology to the used left ie0 exon of AcMNPV, OpMNPV and LdMNPV. Phylogenetic analysis ind icated that the SeMNPV IE1 protein shared the most recent ancestor with its HzSNPV and LdMNPV homologues, although their IE1 proteins had diverged con siderably from each other and from other baculoviruses.