Identification and characterization of Singapore grouper iridovirus (SGIV) ORF162L, an immediate-early gene involved in cell growth control and viral replication

Singapore grouper iridovirus (SGIV) is a major pathogen resulting in heavy economic losses to grouper aquaculture. In this study, SGIV ORF162L encoding a putative homolog of ICP46 was identified and characterized. Interestingly, ICP46 could be found in all sequenced iridoviruses and is considered as a core gene of the family Iridoviridae. SGIV ICP46 was classified as an immediate-early (IE) gene during in vitro infection using drug inhibition analysis, reverse transcription polymerase chain reaction and Western blot analysis. Subcellular localization revealed that SGIV ICP46 was distributed predominantly in the cytoplasm. Furthermore, SGIV ICP46 proved to be a structural protein of the nucleocapsid; its overexpression could promote the growth of grouper embryonic cells and contribute to SGIV replication. This is the first report of the characterization of a putative ICP46 homolog and these results should offer important insights into the pathogenesis of iridoviruses.