The DNA polymerase and helicase genes of a baculovirus of Orgyia pseudosugata.

Regions of the genome of the Orgyia pseudotsugata multinucleocapsid nuclear polyhedrosis virus (OpMNPV) containing the DNA polymerase and helicase genes were sequenced. The DNA polymerase and helicase genes encode predicted proteins of 985 (112.6 kDa) and 1223 (140.5 kDa) amino acids and exhibited 63 % and 59 % amino acid identity, respectively, with their homologues in the Autographa californica MNPV (AcMNPV). The influence of sequence variation between the OpMNPV and AcMNPV DNA polymerase and helicase was investigated by employing gene substitution experiments in transient replication assays in Lymantria dispar and Spodoptera frugiperda cells. The DNA polymerase gene appeared to be interchangeable in this assay; both the AcMNPV and OpMNPV DNA polymerase supported high levels 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 uninfected insect cells. However, the OpMNPV helicase failed to support replication when it replaced the AcMNPV helicase from the set of AcMNPV replication 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 genes.