Transcriptional Analysis of the Gene Encoding the Putative Myristoylated Membrane Protein (ORF458R) of Invertebrate Iridescent Virus 6 (IIV6)

Invertebrate iridescent virus 6 (IIV6) is a member of the genus Iridovirus and belongs to the Iridoviridae family. The entirely sequenced dsDNA genome, composed of 212 482 bp, encodes 215 putative open reading frames (ORFs). ORF458R encodes a putative myristoylated membrane protein. RT-PCR analysis of ORF458R expression in the presence of DNA replication and protein synthesis inhibitors showed that this gene is transcribed in the late phase of the virus infection. Time course analysis showed that transcription of ORF458R initiates between 12 and 24 h p.i. and starts to decrease after this point. Transcription of ORF458R initiated 53 nucleotides upstream of the translation start site and ended 40 nucleotides after the stop codon. Dual luciferase reporter gene assay showed that sequences between ‒61^st and +18^th nucleotides are essential for promoter activity. Interestingly, a remarkable decrease in promoter activity, in the presence of sequences between ‒299^th and ‒143^rd nucleotides, suggested a repressor activity between these regions. Our results showed that ORF458R is transcriptionally active, and separately located sequences at its upstream region with promoter and repressor activities regulating its expression. This information on the transcriptional analysis of ORF458R will contribute to our understanding of the molecular mechanisms of IIV6 replication.