Transcription and temporal cascade in Chilo iridescent virus infected cells

Chilo iridescent virus (CIV) is the type species for genus Iridovirus, and belongs to the family Iridoviridae. Members of this family are large, isometric, cytoplasmic DNA viruses. Our laboratory has established that CIV replicates productively in the cotton boll weevil, Anthonomus grandis. Given the economic importance of this host and the dearth of knowledge on this virus, we have initiated host-virus interaction and molecular studies on CIV. This report focuses on regulation of transcription in CIV infections. We carried out northern analyses on total cellular RNA from infections of IPRI-CF-124T cells, using a complete genomic library of CIV and several putative gene-specific probes. Our data show a temporal cascade based on analysis of 137 detectable transcripts comprising 38 immediate-early (IE), 34 delayed-early (DE), and 65 late (L) transcripts. Analysis with gene-specific probes supported the cascade pattern. Both helicase and RNA polymerase were immediate-early; major capsid protein was late. The CIV gene expression cascade appears to operate primarily at the transcriptional level. Temporal classes observed are consistent with earlier studies at the polypeptide level and with transcriptional patterns in frog virus 3, genus Ranavirus in the Iridoviridae. Our results provide an important basis for understanding mechanisms driving the CIV temporal cascade.