THE DNA-POLYMERASE AND HELICASE GENES OF A BACULOVIRUS OF ORGYIA-PSEUDOTSUGATA

Regions of the genome of the Orgyia pseudotsugata multinucleocapsid nu clear polyhedrosis virus (OpMNPV) containing the DNA polymerase and he licase genes were sequenced. The DNA polymerase and helicase genes enc ode predicted proteins of 985 (112.6 kDa) and 1223 (140.5 kDa) amino a cids and exhibited 63% and 59% amino acid identity, respectively, with their homologues in the Autographa californica MNPV (AcMNPV). The inf luence of sequence variation between the OpMNPV and AcMNPV DNA polymer ase and helicase was investigated by employing gene substitution exper iments in transient replication assays in Lymantria dispar and Spodopt era frugiperda cells. The DNA polymerase gene appeared to be interchan geable in this assay; both the AcMNPV and OpMNPV DNA polymerase suppor ted high level of replication of an origin-containing reporter plasmid when substituted for their homologue and cotransfected with a set of heterologous essential and stimulatory replication genes into uninfect ed insect cells. However, the OpMNPV helicase failed to support replic ation when it replaced the AcMNPV helicase from the set of AcMNPV repl ication genes cotransfected into S. frugiperda cells. In contrast, the AcMNPV helicase gene supported about 50% of the level of replication when substituted for its homologue in the OpMNPV set of replication ge nes.