Identification of the Key Functional Domains of Bombyx mori Nucleopolyhedrovirus IE1 Protein

The immediate early protein 1 (IE1) acts as a transcriptional activator and is essential for viral gene transcription and viral DNA replication. However, the key regulatory domains of IE1 remain poorly understood. Here, we analyzed the sequence characteristics of Bombyx mori nucleopolyhedrovirus (BmNPV) IE1 and identified the key functional domains of BmNPV IE1 by stepwise truncation. Our results showed that BmNPV IE1 was highly similar to Autographa californica nucleopolyhedrovirus (AcMNPV) IE1, but was less conserved with IE1 of other baculoviruses, the C-terminus of IE1 was more conserved than the N-terminus, and BmNPV IE1 was also necessary for BmNPV proliferation. Moreover, we found that IE1(158-208) was a major nuclear localization element, and IE1(1-157) and IE1(539-559) were minor nuclear localization elements, but the combination of these two minor elements was equally sufficient to fully mediate the nuclear entry of IE1. Meanwhile, IE1(1-258), IE1(560-584), and the association of amino acids 258 and 259 were indispensable for the transactivation activity of BmNPV IE1. These results systematically resolve the functional domains of BmNPV IE1, which contribute to the understanding of the mechanism of baculovirus infection and provide a possibility to synthesize a small molecule IE1-truncated mutant as an agonist or antagonist.