Defining the roles of the baculovirus regulatory proteins IE0 and IE1 in genome replication and early gene transactivation

- Separate functions of AcMNPV IE0 and IE1 were determined.
- IE0 and IE1 were expressed under control of identical promoters.
- IE0 and IE1 equally support viral DNA replication and budded virus production.
- Specific viral promoters are more sensitive to transactivation by IE0 than IE1.
- Co-expression of IE0 and IE1 achieves more rapid viral DNA replication.

IE0 and IE1 of the baculovirus Autographa californica multiple nucleopolyhedrovirus are essential transregulatory proteins required for both viral DNA replication and transcriptional transactivation. IE0 is identical to IE1 except for 54 amino acids at the N-terminus but the functional differences between these two proteins remain unclear. The purpose of this study was to determine the separate roles of these critical proteins in the virus life cycle. Unlike prior studies, IE0 and IE1 were analyzed using viruses that expressed ie0 and ie1 from an identical promoter so that the timing and levels of expression were comparable. IE0 and IE1 were found to equally support viral DNA replication and budded virus (BV) production. However, specific viral promoters were selectively transactivated by IE0 relative to IE1 but only when expressed at low levels. These results indicate that IE0 preferentially transactivates specific viral genes at very early times post-infection enabling accelerated replication and BV production.