Transcriptional analysis of the ribonucleotide reductase genes of shrimp white spot syndrome virus

The causative agent of white spot syndrome (WSS) is a large double-stranded DNA virus, WSSV, which is probably a representative of a new genus, provis ionally called Whispovirus. From previously constructed WSSV genomic librar ies of a Taiwan WSSV isolate, clones with open reading frames (ORFs) that e ncode proteins with significant homology to the class I ribonucleotide redu ctase large (RR1) and small (RR2) subunits were identified. WSSV rr1 and rr 2 potentially encode 848 and 413 amino acids, respectively. RNA was isolate d from WSSV-infected shrimp at different times after infection and Northern blot analysis with rr1- and rr2-specific riboprobes found major transcript s of 2.8 and 1.4 kb, respectively, 5' RACE showed that the major rrl transc ript started at a position of -84 (C) relative to the ATG translational sta rt, while transcription of the rr2 gene started at nucleotide residue -68 ( T). A consensus motif containing the transcriptional start sites for rr1 an d rr2 was observed (TCAc/tTC). Northern blotting and RT-PCR showed that the transcription of rr1 and rr2 started 4-6 h after infection and continued f or at least 60 h. The rr1 and rr2 genes thus appear to be WSSV "early genes ." (C) 2000 Academic Press.