Host range expansion of Autographa californica nuclear polyhedrosis virus (NPV) following recombination of a 0.6-kilobase-pair DNA fragment originating from Bombyx mori NPV.

We have isolated hybrid baculoviruses of Bombyx mori nuclear polyhedrosis virus (BmNPV) and Autographa californica NPV (AcNPV) capable of replicating in both BmN (not susceptible to AcNPV) and SF-21 (not susceptible to BmNPV) cells (A. Kondo and S. Maeda, J. Virol. 65:3625-3632, 1991). Repeated backcross infection of one of these recombinant isolates with AcNPV generated eh-AcNPV, a virus with restriction endonuclease patterns of genomic DNA nearly identical to those of AcNPV but capable of replicating in both BmN and SF-21 cells, i.e., host range expanded. Expanded host range viruses were also isolated following cotransfection of AcNPV DNA with eh-AcNPV DNA cleaved with either HindIII or PstI. Subsequent cotransfection of AcNPV DNA with plasmids from an eh-AcNPV DNA fragment library identified an 11-kbp HindIII fragment that could expand the host range of AcNPV. Subcloning and cotransfection analyses localized a 572-bp SacI-HindIII fragment within this 11-kbp fragment which could alone expand the host range of AcNPV. Mapping and nucleotide sequencing analysis revealed that this fragment was identical to the corresponding 572-bp fragment (BmScH) of BmNPV. Furthermore, this fragment originated from the coding region of the putative DNA helicase gene. Cotransfection of AcNPV DNA with BmScH also generated a host range-expanded virus, eh2-AcNPV. These results indicated that the expanded host range characteristics of eh2-AcNPV were solely the result of recombination within the coding region of the putative DNA helicase gene.