Analysis of baculovirus genomes with restriction endonucleases.

The viral DNAs from nine wild-type insect baculoviruses have been isolated and the EcoR-1 restriction endonuclease fragment patterns compared. Genomic heterogeneity could be detected in the DNA restriction patterns of four of these wild-type baculoviruses. Three infectious virus forms (two that are occluded in the nucleus and an extracellular virus that has budded from the plasma membrane of infected cells) of a nuclear polyhedrosis virus with multiple nucleocapsids per envelope (MNPV) from the lepidopteran insect, Autographa californica are shown to be phenotypically distinct by comparison of viral structural polypeptides by polyacrylamide gel electrophoresis and autoradiography of L[35S]methio-nine-labeled virus proteins. The three phenotypic forms were cloned by successive plaque purification and eight distinct variants were identified from 11 plaque-purified viruses by genotypec analysis with EcoR-1 and HindIII restriction endonuclease. Isolation of variants from the three phenotypic forms has shown that each of the infectious forms is heterogeneous and that no segregation of genotypes among the three forms was evident. The characteristic restriction fragment patterns of several variants were maintained upon multiple passage in cell culture.