Transcriptional regulation of the channel catfish virus genome direct repeat region

Channel catfish virus (CCV), a member of the herpesvirus family, causes a s evere haemorrhagic disease in juvenile channel catfish. In this report, we confirm that CCV gene expression is temporally regulated into immediate-ear ly (IE), early and late phases, similar to that of other herpesviruses. The transcriptional regulation of the 14 genes within the direct repeat region of the CCV genome was determined by Northern hybridization analysis of RNA isolated from infected cells in the presence or absence of metabolic inhib itors. Two CCV genes within the direct repeat, ORFs 1 and 3, expressed IE t ranscripts. Early RNAs were encoded by ORFs 2-9 and 11-14. ORFs 4, 7 and 10 -13 expressed late transcripts after the onset of viral DNA replication. A time-course study conducted without metabolic inhibitors confirmed that CCV direct repeat transcription is temporally regulated. The characterization of CCV transcription during cytolytic infection in vitro will provide a fou ndation for the analysis of CCV gene expression in tissues of acutely and l atently infected catfish.