| Summary: Programmed cell death or apoptosis is a major defense mechanism used by insects in response to viral infections. Viruses can only successfully infect the host if they inhibit this apoptosis. The genome of Chilo iridescent virus (CIV) has three ORFs with homology to baculovirus inhibitor of apoptosis (iap) genes. The proteins encoded by the 157L, 193R, and 332L genes contain 152, 208 and 234 amino acids, respectively, and shares homology to the IAP-3 protein of Cydia pomonella granulovirus. The protein encoded by ORF 193R contains a BIR motif (baculoviral iap repeat) in the amino-terminal segment and a carboxy-terminal RING finger motif. The presence of a BIR domain in a CIV open reading frame is a unique feature among Iridoviridae. Transcriptomic analysis of the gene by RT-PCR allowed us to determine the transcription start point and 5` UTR region of the gene. Transcription class was determined in infection of Bombyx mori cells in the presence of inhibitors of DNA or protein synthesis and showed that CIV iap is an immediate-early gene.
Transcription of the CIV iap gene initiated 18 nt upstream of the translational start site. When this putative CIV iap was transiently expressed in SPC-BM-36 and Sf21 cells under control of an early baculovirus promoter (ie1), it blocked apoptosis induced by actinomycin-D. RNA interference was used to knockdown the expression of 193R during CIV infection in SPC-BM-36 cells. The conclusion from these results is that CIV ORF 193R encodes a functional IAP protein.
Keywords: Chilo iridescent virus, inhibitor of apoptosis, RNA interference, Functional genomics. |
