Homologous region 1 of Plutella xylostella granulovirus functions as an enhancer for early gene expression

Homologous regions (hrs) contained in genomes of baculoviruses have been shown to function as origins of viral DNA replication in alphabaculoviruses and betabaculoviruses, and as enhancers for early gene expression in alphabaculoviruses. The hr sequences of betabaculoviruses differ substantially from the ones of alphabaculoviruses. The enhancing property of betabaculovirus hrs has not been reported. In this study, transient assays were performed to investigate the effects of Plutella xylostella granulovirus (PlxyGV) hr1 on early gene expression of the virus. It was shown that hr1 stimulated reporter gene expression from the promoters of four early genes – ie1, dnapol, lef1, and lef9 – independent of additional viral gene expression. The PlxyGV ie1 was shown to repress reporter gene expression from all four early gene promoters in a Trichoplusia ni cell line, both in the presence and absence of hr.