Baculovirus (MNPV) genomic variants: characterization of Spodoptera exempta MNPV DNAs and comparison with other Autographa californica MNPV DNAs.

A nuclear polyhedrosis virus (NPV) strain from Spodoptera exempta (SeMNPV-25 baculovirus) is a restriction endonuclease DNA map variant similar to Autographa californica NPV (AcMNPV baculovirus). Fourteen restriction endonuclease variants were identified and isolated from a SeMNPV baculovirus stock with 12 of the variants found at low frequency (less than 3%). The DNA from each variant was compared to the prototype SeMNPV-25 for insertions, deletions and new restriction sites. Regions of variation were defined on the prototype SeMNPV-25 genome, and the nature of the variation within these regions was determined. These data are discussed and compared with the existing data on other variants of AcMNPV. A comparison of the physical maps revealed that all the SeMNPV variants were different from those reported for AcMNPV. Although the SeMNPV variants were distinctive, they were clearly genomic AcMNPV variants. The regions of the baculovirus genomic variation were identified, and three separate mechanisms are suggested for their generation. Five regions (hr1 to hr5) were associated with intragenic homologous viral sequences, five regions (vI to vIII) may be associated with the insertion of DNA sequences of cellular origin, and two regions (pI and pII) were associated with mutations resulting in the addition or loss of a PstI site. Physical maps were generated for SeMNPV variant regions vI, hr2, vII and vIII.