Identification of lef-7: a baculovirus gene affecting late gene expression

We have examined a 15-kb region of the Autographa californica nuclear polyhedrosis virus (AcMNPV) genome, from 66 to 78 map units, for the presence of genes which transactivate expression from late and very late viral promoters in transient expression assays. One gene in this region activated reporter gene expression approximately six- to eightfold when the reporter gene was under the control of the late promoter of the major capsid protein gene, vp39, or the very late promoter of the polyhedrin gene, polh, but not when the reporter gene was under the control of the early promoter of etl, a homolog of proliferating cell nuclear antigen. The sequence of the predicted polypeptide product of this gene, lef-7, shared no obvious sequence homology to other sequences in available databases. Transcriptional analysis indicated that lef-7 was transcribed early in infection from an initiation site 14 to 16 bp upstream of the putative translational start site and was also transcribed late in infection from an initiation site(s) further upstream. The lef-7 promoter and the promoter of another previously defined late expression factor, lef-3, were both dependent on the multifunctional transregulatory gene, ie-1, for activity in transient expression assays. While sequencing the region of the AcMNPV genome containing lef-7, we also found a 215-codon open reading frame (ORF-215) approximately 1 kb downstream of lef-7 with sequence homology to eIF2 alpha kinases (e.g., rabbit eIF2 alpha and yeast GCN-2 kinase). However, only the six C-terminal conserved domains of protein kinases were present in the predicted ORF-215 product and several of these domains varied from the consensus sequence. ORF-215 did not strongly influence expression from the vp39 promoter-controlled reporter gene in the transient expression assays employed.