Identification and characterization of a shrimp white spot syndrome virus (WSSV) gene that encodes a novel chimeric polypeptide of cellular-type thymidine kinase and thymidylate kinase

From previously constructed genomic libraries of a Taiwan WSSV isolate, a p utative WSSV tk-tmk gene was identified. Uniquely, the open reading frame ( ORF) of this gene was predicted to encode a novel chimeric protein of 388 a mino acids with significant homology to two proteins: thymidine kinase (TK) and thymidylate kinase (TMK). Northern blot analysis with a WSSV tk-tmk-sp ecific riboprobe detected a major transcript of 1.6 kb. When healthy adult Penaeus monodon shrimp were inoculated with WSSV, the tk-tmk gene transcrip t was first detected by RT-PCR analysis at 4 h postinfection and transcript ion levels continued to increase over the first 18 h. The gene's major in v itro transcription and translation product, equivalent to the predicted siz e (43 kDa), is a single chimeric protein that includes both the TK and TMK functional motifs. Evidence for phylogenetic analysis and sequence alignmen t suggested that the gene may have resulted from the fusion of a cellular-t ype TK gene and a cellular-type TMK gene. Its unique arrangement may also p rovide a valuable gene marker for WSSV. (C) 2000 Academic Press.