Transcriptional mapping in Chilo iridescent virus infections

Abstract

Chilo iridescent virus (CIV) belongs to the family Iridoviridae, which are icosahedral cytoplasmic DNA viruses with large, linear, and circularly permuted genomes. Previous studies on infected-cell-specific polypeptides suggested temporal regulation of CIV gene expression. Recently, we demonstrated three temporal classes at the transcriptional level, in CIV infections of a spruce budworm cell line. We also demonstrated a transcriptional cascade with positive and negative control. In this paper, we assign all detectable viral transcripts into respective temporal classes and map them using restriction fragments from a genomic library. More than 90 percent of the genome is transcriptionally active with at least four major clusters of immediate-early transcription and at least three delayed-early clusters. Late transcripts were observed throughout the genome. There was at least one exclusive region in the genome for each of the three temporal classes. We correlated transcribed regions with ORFs on the CIV genome and showed that known ORFs in the exclusive regions are generally consistent with phase-specific requirements of large DNA viruses. Our data also suggest the presence of 5' or 3' coterminal transcripts. This is the first complete transcription map for a member of the genus Iridovirus.

Transcription Program of Red Sea Bream Iridovirus as Revealed by DNA Microarrays

“…In these studies, the second class is called delayed-early. For example, in CIV infection, 37 transcripts were classified as IE, 35 transcripts as DE, and 65 transcripts as L (12). Thus, the temporal expression kinetics observed in RSIV are similar to those observed in other iridoviruses, suggesting that they are a common feature of the family Iridoviridae.…”

“…These results are similar to those observed in other members of the family Iridoviridae. IE transcripts of CIV were also not clustered in any specific regions in the CIV genome, DE transcripts were clustered in at least three DE discrete regions, and L transcripts were distributed throughout the genome (12). IE transcripts originated from at least one third of the genome in FV3 (57) and from seven different regions in Wiseana iridescent virus (36).…”

“…2A and B). Three temporal kinetic classes of transcripts have also been identified in FV3, CIV, and Wiseana iridescent virus infections (8,12,36,61). In these studies, the second class is called delayed-early.…”

“…and showed peak levels between 3 h to 12 h p.i. L transcripts were detected either at 6 h, 12 h, or 24 h p.i (11,12). In the transcription program of HHV-8, genes involved in gene regulation or IE genes showed the earliest increase in expression.…”

Genomic Sequence of Spodoptera frugiperda Ascovirus 1a , an Enveloped, Double-Stranded DNA Insect Virus That Manipulates Apoptosis for Viral Reproduction

“…Other intergenic regions did not contain lower GϩC peaks, indicating that two types of putative intergenic regions were present in SfAV: GϩC-rich and GϩC-poor regions. Data published previously on transcription of CIV indicate that genes are transcribed temporally as mono-or polycistronic mRNA (31), suggesting that the GϩC-poor regions delineate regions in which transcription is arrested at the termination of mRNA synthesis. In agreement with previous ascovirus sequence analyses (97), we observed that all GϩC-poor regions contained short inverted repeats that might function as transcription termination signals.…”