Patterns of genome organization and content in lepidopteran baculoviruses

With the completion of the genome sequences of a number of highly diverse lepidopteran baculoviruses including five NPVs and two GVs, patterns of genome organization and structure are emerging. The circular, supercoiled, double-stranded DNA genomes are punctuated by sets of homologous regions, which likely play a major role as enhancers of transcription, replication origins, and genome processing signals. These studies have also revealed a set of 67 genes that are shared between all these viruses. Sixteen of these genes are likely involved in replication and transcription (six replication, eight late transcription-specific, and vlf-1 and alkaline nuclease) and comprise almost 25% of the conserved genes (Table 3). Another major group of genes is those associated with virion structure. These also comprise almost 25% of the conserved genes (Table 3). A number of other genes are also common to baculovirus genomes including homologs of sod, fgf, and ubiquitin suggesting common patterns of interaction with host cells. These viruses have much in common, but they also encode a great variety of genes, either unique to each virus or shared with a subset of the other baculoviruses. The accumulation of sequence data has revealed a wealth of information concerning the extent of variation and conservation of baculovirus genomes. With this basic information, we can now attempt to understand how these different combinations of genes influence features of infection such as the range of hosts and tissues infected, the extent of dependence on and interaction with host enzymes, and the efficiency of replication.