Identification and characterization of lef-1, a baculovirus gene involved in late and very late gene expression.

An Autographa californica nuclear polyhedrosis virus (AcMNPV) gene required in transient expression assays for late and very late viral gene expression was identified, sequenced, and transcriptionally mapped. This gene, designated late expression factor 1 (lef-1), was located between 7.4 and 8.7 map units of the AcMNPV physical map. It was identified by cotransfecting Spodoptera frugiperda cultured cells with a collection of overlapping cloned DNA fragments covering the entire AcMNPV genome and a reporter gene controlled by an early, late, or very late AcMNPV promoter. Omission of the DNA fragment containing lef-1 curtailed most late and very late gene expression but not early gene expression. lef-1 was found to be an early gene transcribed as a 1.8-kb RNA in the presence of the protein synthesis inhibitor cycloheximide. The C terminus of the predicted polypeptide product, LEF-1, contained a sequence motif characteristic of nucleoside triphosphate-binding sites.