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Defining the role of autographa californica multiple nucleopolyhedrovirus immediate early-0 and immediate early-1 proteins in viral genome replication and early gene transactivation

University of British Columbia

The immediate early-0 (IE0) and IE1 proteins of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) are key transregulators in the viral replication cycle. If both proteins are absent, the virus is inactive. Either protein can support viral replication but both are required to achieve wildtype infection. Both IE0 and IE1 are involved in viral DNA replication and transcriptional transactivation of early genes. In this study, to analyze IE0 and IE1’s function, ie0, ie0MtoA or ie1 were placed under the control of identical promoters (ie1 or gp64) to achieve comparable levels of protein expression. The ie1 promoter produced higher levels of IE0, IE0MtoA and IE1 compared to the gp64 promoter. Time course assays of infected Spodoptera frugiperda 9 (Sf9) cells allowed examination of viral DNA replication and budded virus (BV) production. The results showed that when IE0 and IE1 protein levels were high, either IE0, IE1 or IE0 and IE1 together maintained DNA replication and BV production similar to wildtype levels. However, when IE0 and IE1 protein levels were low, only when IE0 and IE1 were present together was DNA replication and BV production similar to wildtype. These results suggest that during the virus replication cycle when cellular levels of IE0 or IE1 are low, for example at the beginning of infection, the presence of both proteins results in more efficient DNA replication. Transient transactivation studies were also performed to examine IE0 and IE1’s ability to activate nineteen viral early gene promoters. At low levels of IE0 and IE1 expression, a group of viral early gene promoters were found to be differentially transactivated by IE0 alone or when both IE0 and small amounts of IE1 were together. These results suggest that during early times post-infection, when cellular levels of viral proteins are low, IE0 in the presence of a small amount of IE1 results in rapid onset of viral DNA replication and efficient transactivation of a specific set of viral early gene promoters. In context of virus infection, rapid viral replication by IE0 and IE1 and transactivation of early genes by IE0 may counter the insect’s defense mechanisms like sloughing and apoptosis.

Text

2012-08-14

Attribution-NonCommercial-NoDerivs 3.0 Unported

http://hdl.handle.net/2429/42940

Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/3.0/