Functional analysis of evolutionary conserved clustering of bZIP binding sites in the baculovirus homologous regions (hrs) suggests a cooperativity between host and viral transcription factors.

The genome of the Autographa californica Multinucleocapsid Polyhedrosis Virus (AcMNPV) contains nine interspersed homologous regions (hrs) that function as potent enhancer sequences when linked in cis to either viral or heterologous RNA polymerase II-dependent promoters. Their activity is strongly increased by the binding of the major immediate early viral transregulator IE1 on 28-mer palindromic sites present in hrs. We show that hrs of AcMNPV additionally carry, in the interpalindromic sequences, a large number of cAMP response elements (CRE) and TPA response elements (TRE), known to bind ubiquitous cellular transcription factors of the bZIP family. Moreover, these clusters of CRE and TRE motifs are concentrated in hrs. Analysis of the 25 baculovirus genomes sequenced so far reveals that these motifs are evolutionary conserved in Lepidoptera NPVs, suggesting a functional role in the hr enhancer function. Consistently, EMSA experiments indicate that CRE and on a lesser extent TRE sites specifically bind insect host factors. Moreover, reporter assays reveal that these CRE sites have an additive stimulatory effect on RNAPol II-dependent transcription in Sf9 cells and are potentially able to synergize with the IE1-binding palindrome.

Characterization and transcriptional profiles of three Spodoptera frugiperda genes encoding cysteine-rich peptides. A new class of defensin-like genes from lepidopteran insects?

The present work describes sequence and transcription of three Spodoptera frugiperda genes encoding 6-cysteine-rich peptides. Sequence alignments indicate that the predicted peptides belong to the insect defensin family, although phylogenetic analyses suggest they form a cluster distinct from that of other neopteran insect defensins. The three genes were identified in a non-immune-challenged Sf9 cells cDNA (DNA complementary to RNA) library (Landais et al., Bioinformatics, in press) and were named spodoptericin, Sf-gallerimycin and Sf-cobatoxin. Spodoptericin is a novel defensin-like gene that appears to be weakly up-regulated following injection of bacteria and fungi. Interestingly, no sequence motif clearly homologous to cis regulatory element involved in the regulation of antimicrobial genes was found. An homologue of the spodoptericin gene was identified in the SilkBase Bombyx mori cDNA library. Sf-gallerimycin is related to the Galleria mellonella gallerimycin gene and is induced after immune challenge by injection of bacteria in the larval fat body as well as in hemocytes. In silico analysis of the sequence upstream from the cDNA reveals the presence of at least one motif homologous to a nuclear factor kappaB (NF-kappaB) binding site. Finally, Sf-cobatoxin is related to the G. mellonella cobatoxin-like gene. Despite high levels of constitutive expression compared to the two previous genes, transcription of Sf-cobatoxin is increased after immune, in particular, bacterial challenge. We therefore confirm that these three genes encode potential candidate molecules involved in S. frugiperda innate humoral response.