Functional dissection of the Autographa californica nuclear polyhedrosis virus immediate-early 1 transcriptional regulatory protein.

Autographa californica multicapsid nuclear polyhedrosis virus-infected insect cells express a viral immediate-early transcriptional regulatory protein, IE1, that has been shown by transient-expression assays to stimulate the expression of certain baculovirus delayed-early (DE) promoters and to inhibit the expression of other immediate-early (IE) genes. It is believed that certain DE promoters are activated, in part, by direct interactions between IE1 and enhancer elements located in regions adjacent to these genes. We have used transient cotransfection and DNA-binding assays to examine the function of mutant forms of IE1. Our results indirectly show that IE1 has at least two separable domains that are essential for its role in the modulation of baculovirus gene expression. A domain rich in acidic residues and essential for transactivation is located within the N-terminal 145 amino acids of the polypeptide. A second domain, located in the C-terminal 437 amino acids of IE1, is required for inhibitory and DNA-binding activities. Several nontransactivating IE1 mutants trans-dominantly interfered with wild-type IE1 transactivation of enhancer-linked DE genes. trans-dominant interference was expressed only by IE1 mutants that retained the N-terminal putative acidic activation domain, suggesting that this region may be involved in associations with a factor(s) essential for activation of enhancer-linked genes.