Novel regulatory properties of the IE1 and IE0 transactivators encoded by the baculovirus Autographa californica multicapsid nuclear polyhedrosis virus

Abstract

The baculovirus Autographa californica multicapsid nuclear polyhedrosis virus expresses two immediateearly genes from the HindIII-G region (map units 90.4 to 96.8) of the genome. During the early phase of infection, nonspliced 1.9-kb and spliced 2.1-kb transcripts are expressed which encode the IEl and IEO (spliced IEI) gene products, respectively. These two gene products differ only in that IEO contains an additional 54 amino acids at the amino terminus. RNA analysis of these two genes during infection revealed that they were differentially expressed. IE1 was expressed early and late, whereas IEO was expressed only early in infection. The regulation of these two immediate-early genes was analyzed by transient expression assays. The IEl gene product stimulated expression of IEI promoter-directed expression but down-regulated expression from the IEO promoter. The IEO gene product also transactivated the IEl promoter but did not affect expression from its own promoter. Unlike IEl, which transactivates the delayed early 39K gene in the presence and absence of the homologous region (hr) enhancers, IEO transactivated the 39K promoter only in the presence of cis-linked hr5 enhancer. The results of this study in conjunction with previous results suggest that the IEl gene encodes a multifunctional gene product that may be involved in (i) repression of immediate-early gene expression, (ii) continued expression of its own gene product during infection, and (iii) transactivation of the delayed early and late classes of genes.

The Baculoviruses Occlusion‐Derived Virus: Virion Structure and Function

“…IE-1 also colocalizes with VP39 in the virogenic stroma (Kawasaki et al, 2004) and thus is present in regions of capsid assembly. The ie-1 gene is strongly expressed early in infection and its transcripts can be detected within 20 minutes postinfection (Kovacs et al, 1991). One the potential roles of nucleocapsid-associated IE-1 may be to transcriptionally activate the expression of early viral genes immediately after the genome has been unpackaged in the nucleus of a new host cell.…”

“…PNK/PNL could be involved in the RNA splicing and repair activities that occur with the expression of the immediate early transcription factor gene ie0. The ie0 gene is the only known early baculovirus gene to be spliced (Kovacs et al, 1991;Pearson and Rohrmann, 1997;Theilmann et al, 2001) and it plays an essential role establishing baculovirus infection (Pearson and Rohrmann, 1997;Stewart et al, 2005). The ie0 gene results from the splicing of a small exon onto the 5 0 end of the ie-1 gene (Chisholm and Henner, 1988).…”

“…The ie0 gene results from the splicing of a small exon onto the 5 0 end of the ie-1 gene (Chisholm and Henner, 1988). Expression of ie0 occurs very rapidly in the first few hours of infection and then diminishes while ie-1 expression continues late into the virus replication cycle (Kovacs et al, 1991). At the beginning of infection, there is likely an immediate need for robust RNA-splicing activities to ensure translation of IE0.…”

Expression of PE38 and IE2, viral members of the C3HC4 finger family, during baculovirus infection: PE38 and IE2 localize to distinct nuclear regions

“…The gene product IE1 has been shown to transactivate several early, late, and very late promoters (13,14,26,31), while IE2 augments expression from these promoters (5,6,31,46). Furthermore, IE1 is able to inhibit expression of the ie2 and ie0 promoters (7,21). The putative regulatory functions of other early viral genes like pe38 (23), me53 (19), and cg30 (39) are based on sequence analysis.…”

In Vivo and In Vitro Analysis of Baculovirus ie-2 Mutants

“…Four genes of the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) are known to trans activate early baculovirus promoters in transient expression assays: ie-0 (5,17), ie-1 (11,12), ie-2 (3,4), and pe-38 (18,20). IE-1, the product of ie-1, is the most thoroughly characterized trans regulator of AcMNPV and is thought to play a central role in the regulation of early gene expression and possibly DNA replication (8).…”