Genomic organization of Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus

The genome organization of the Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus (HearNPV) was investigated and compared to that of other baculoviruses. A detailed physical map was constructed for the restriction enzymes BamHI, BglII, EcoRI, HindIII, KpnI, PstI, SacI and XhoI. The 130.1-kilobase pairs (kb) long viral genome was cloned as restriction fragments into a plasmid library, which covered 97.5% of the viral genome. From this plasmid library about 45 kb of dispersed sequence information was generated. Fifty-three putative open reading frames (ORFs) with homology to ORFs of other baculoviruses were identified and their location on the genome of HearNPV was determined. The arrangement of the ORFs along the HearNPV genome is significantly different from the multiple-nucleocapsid NPVs, AcMNPV, BmNPV and OpMNPV, which have a highly collinear genome, and the granulovirus XcGV. In contrast the genomes of HearNPV and SeMNPV are highly collinear. This close relatedness between an MNPV and an SNPV is supported by the phylogeny of specific genes of these two viruses and suggests that the morphotype (S or M) is only a taxonomic and not a phylogenetic denominator. The data presented here also give further support to the view that the gene distribution along baculovirus genomes can be used as a character to describe baculovirus relatedness independent of gene phylogeny. Five homologous regions (hrs) were located on the genome of HearNPV. This is also the first report of the existence of hrs in SNPVs and this observation suggests that hrs are a common feature of baculovirus genomes.