Rana grylio virus thymidine kinase gene: an early gene of iridovirus encoding for a cytoplasmic protein
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The presence of thymidine kinase (TK) is a feature of many large DNA viruses. Here, a TK gene homologue was cloned and characterized from Rana grylio virus (RGV), a member of family Iridoviridae. RGV TK encodes a protein of 195 aa with a predicted molecular mass of 22.1 kDa. Homologues of the protein were present in all the currently sequenced iridoviruses, and phylogenetic analysis showed that it was much close to cellular TK type 2 (TK2), deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK). Subsequently, Western blotting revealed TK expression increased with time from 6 h post-infection in RGV-infected cells. Using drug inhibition analysis by protein synthesis inhibitor (cycloheximide) and DNA replication inhibitor (cytosine arabinofuranoside), RGV TK was classified as the early expression gene during in vitro infection. Subcellular localization by TK–GFP fusion protein expression and immunofluorescence staining showed RGV TK was an exclusively cytoplasmic protein in fish cells. Collectively, current data indicate that RGV TK was an early gene of iridovirus which encoded a cytoplasmic protein in fish cells.
KeywordsRana grylio virus (RGV) Iridovirus Thymidine kinase Early viral gene Cytoplasmic protein
This work was supported by grants from the National Major Basic Research Program (2004CB117403), the National 863 High Technology Research Foundation of China (2006AA09Z445, 2006AA100309 and 20060110A4013), the National Natural Science Foundation of China (30671616 and U0631008), and the Key Technology R & D Program of China (2006BAD03B05).
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