An additional copy of the homologous region (hr1) sequence in the Autographa californica multinucleocapsid polyhedrosis virus genome promotes hyperexpression of foreign genes

The Autographa californica multinucleocapsid nuclear polyhedrosis virus genome contains nine homologous region (hr1, hr1a, hr2, hr2a, hr3, hr4a, hr4b, hr4c, and hr5) sequences that are thought to be involved in viral replication and activation of transcription. Our results show that the 750 bp hr1 sequence is capable of functioning as an enhancer of transcription of foreign genes from the homologous late polyhderin gene promoter and the heterologous Drosophila heat shock protein (hsp70) promoter in insect cells. Introduction of an additional copy of the complete hr1 element downstream to the polyhedrin locus in the viral genome, while not affecting the stability of the recombinant virus for at least 30 serial passages, led to hyperexpression of reporter genes. The enhancement in the expression levels of foreign genes varied from 40 to 90-fold depending on the promoter used.