Chilo iridescent virus (CIV), the type species of the genus Iridovirus, a member of the Iridoviridae family, is highly pathogenic for a variety of insect larvae. The virions contain a single linear
ds DNA molecule that is circularly permuted and terminally redundant. The coding capacity and strategy of the CIV genome was elucidated by the analysis of the complete
DNA nucleotide sequence of the viral genome (212,482 bp) using cycle sequencing by primer walking technology. Both
DNA strands were sequenced independently and the average redundancy for each
nucleotide was found to be 1.85. The base composition of the viral genomic DNA sequence was found to be 71.37% A+T and 28.63% G+C. The CIV genome contains 468 open reading frames (ORFs). The size of the individual
viral gene products ranges between 40 and 2432
amino acids. The analysis of the coding capacity of the CIV genome revealed that 50% (234 ORFs) of all identified ORFs were nonoverlapping. The comparison of the deduced amino acid sequences to entries in
protein data banks led to the identification of several genes with significant homologies, such as the two major subunits of the
DNA-dependent
RNA polymerase,
DNA polymerase,
protein kinase,
thymidine and
thymidylate kinase,
thymidylate synthase,
ribonucleoside-diphosphate reductase, major
capsid protein, and others. The highest homologies were detected between putative
viral gene products of CIV and lymphocystis
disease virus of fish (LCDV). Although many CIV putative gene products showed significant homologies to the corresponding
viral proteins of LCDV, no colinearity was detected when the coding strategies of the CIV and LCDV-1 were compared to each other. An intriguing result was the detection of a viral
peptide of 53
amino acid residues (ORF 160L) showing high homology (identity/similarity: 60.0%/30.0%) to
sillucin, an
antibiotic peptide encoded by Rhizomucor pusillus. Iridovirus homologs of cellular genes possess particular implications for the molecular evolution of large DNA viruses.