IMMEDIATE-EARLY TRANSCRIPTION FROM THE CHANNEL CATFISH VIRUS GENOME -CHARACTERIZATION OF 2 IMMEDIATE-EARLY TRANSCRIPTS

With cDNA probes and by Northern (RNA) blot analysis, a region contain ing immediate-early (IE) genes in the channel catfish virus (CCV) geno me was identified. IE transcription in CCV-infected cells appears to b e restricted to the terminal repeat region, suggesting that CCV is mos t closely related to the alpha subfamily of herpesviruses. CCV DNA fra gments from this region encoding IE transcripts were cloned. Northern analysis with one of these cloned fragments, a 3,927-bp EcoRI-XbaI fra gment, indicates that it encodes two IE transcripts. Both transcripts (ie1 and ie2) were characterized by S1 nuclease analysis, primer exten sion analysis, and analysis of cDNAs. The ie2 transcript is a 1,3-kb b icistronic mRNA containing open reading frame (ORF) 8a and ORF 9. ORF 8a is a 5'-truncated version of ORF 8 which, along with ORF 9, was pre viously identified (A.J. Davison, Virology 186:9-14, 1992). The ie1 tr anscript is 0.6 kb in size, contains only ORF 9, and is expressed at a level approximately six times that of ie2 in cycloheximide-treated ce lls. The putative product of ORF 9 is predicted to have a basic pI and contains a potential zinc-binding domain, making it a probable transc ription factor. ORF 8a encodes a putative product which is very hydrop hobic, an unusual characteristic for an IE protein.