Identification, sequence, and transcriptional analysis of lef-3, a gene essential for Orgyia pseudotsugata baculovirus DNA replication.

Using a transient complementation assay for DNA replication of an origin-containing reporter plasmid, a 2.4-kb region (m.u. 48.3-50.1) of the Orgyia pseudotsugata multinucleocapsid nuclear polyhedrosis virus (OpMNPV) genome was identified that contains a gene essential for OpMNPV DNA replication. This region was sequenced and open reading frames were identified. Replication assays using subclones from this region identified a gene called late expression factor 3 (lef-3), as the essential replication gene. Transcriptional mapping using both Northern blot and S1 nuclease protection assays demonstrated that lef-3 was expressed as an early gene with a major transcript of 1.7 kb in length. OpMNPV lef-3 encodes a protein with a predicted molecular weight of 42.6 kDa (373 amino acids) and exhibits 41% amino acid sequence identity with its homolog in the genome of the Autographa californica MNPV. A pattern of amino acids similar to that found in single-stranded DNA binding proteins is present in the amino-terminus of both OpMNPV and AcMNPV LEF-3.