Identification of a Bohle iridovirus thymidine kinase gene and demonstration of activity using vaccinia virus

In recent years interest in the family Iridoviridae has been renewed by the identification of a number of viruses, particularly from the genus Ranavirus, associated with disease in a range of poikilotherms. Ranaviruses have been isolated from amphibian, piscine and reptilian species. Here we describe an open reading frame (ORF) identified in the genome of Bohle iridovirus (BIV) which contains a nucleotide binding motif conserved within the thymidine kinase (TK) genes of iridoviruses from other genera (lymphocystis disease virus, LCDV, type species of the genus Lymphocystivirus; Chilo iridescent virus, CIV, type species of the genus Iridovirus). The ability of this putative gene to express a functional TK was confirmed by rescue of a TK negative mutant vaccinia virus in the presence of selective media, when expression was controlled by a vaccinia virus promoter. The sequence of the BIV TK was compared with the homologous sequences from epizootic haematopoietic necrosis virus (EHNV), a virus associated with disease in fish, from Wamena iridovirus (WIV) associated with systemic disease in green pythons, and from frog virus 3 (FV3) the ranavirus type species. Comparisons between these sequences and those available from other ranaviruses, other iridoviruses, other DNA viruses and cellular TKs are presented.