Available online at www.sciencedirect.com Virus Research 129 (2007) 135–144 Characterization of a late gene encoding for MCP in soft-shelled turtle iridovirus (STIV) Zenglian Zhao a,e,1 , Yong Teng b,1 , Hong Liu c , Xiangmei Lin d , Kan Wang c , Yulin Jiang c , Huanchun Chen e,∗ a General Administration of Quality Supervision, Inspection and Auarantine of the People’s Republic of China, Beijing 100088, PR China b State Key Laboratory of Biocontrol, School of Life Sciences of Sun Yat-sen University, Guangzhou 510275, PR China c Shenzhen Exit & Entry Inspection and Quarantine Bureau, Shenzhen 518001, PR China d Chinese Academy of Inspection and Quarantine, Beijing 100088, PR China e State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, PR China Received 5 April 2007; received in revised form 2 July 2007; accepted 3 July 2007 Available online 16 August 2007 Abstract Major caspid protein (MCP) is the major structural component of virus particles and revealed to be very responsible for classification of new tentative iridovirus isolates. In this paper, the complete sequences of MCP gene was firstly identified and characterized from soft-shelled turtle iridovirus (STIV). The MCP, classified as a late transcript by drug inhibition, encodes a protein of 463 aa with a predicted molecular weight of 50 kDa. Indirect immunofluorescence (IIF) and virus neutralization assay were developed to determine the sensitivity and virus neutralizing activity of MCP-specific antiserum. Furthermore, the MCP temporal expression pattern during STIV infection in vitro was characterized by Western blot and RT-PCR assays. The results suggest that STIV could be classified as a member of genus Ranavirus in family Iridoviridae and has cell-type-specific programs of viral gene expression. © 2007 Elsevier B.V. All rights reserved. Keywords: Soft-shelled turtle iridovirus (STIV); Ranavirus; Major caspid protein (MCP); Late viral gene; Temporal expression pattern 1. Introduction Outbreak of a novel viral disease called ‘red neck disease’ resulted in high mortality in cultured soft-shelled turtle (Tri- onyx sinensis) in China, was firstly reported in 1998 (Chen et al., 1998). The infectious pathogen was originally isolated from the organs of these diseased turtles. Then based on histopathological and morphological evidences, this virus was characterized as a member of family Iridoviridae tentatively based on histopathological and morphological evidences, and designated as soft-shelled turtle iridovirus (STIV) (Chen et al., 1999). This virus could replicate and cause cytopathic effect (CPE) at 15–30 ◦ C in several fish cell lines, such as grass carp overy ∗ Corresponding author. Tel.: +86 27 87280470; fax: +86 27 87282608. E-mail address: chench 2007@yahoo.com.cn (H. Chen). 1 These authors contributed equally to this work. (CO), fathead minnow (FHM), carp kidney (CK) and grass carp kidney (GCK) cells. Among them, the virus could cause rapid CPE and high titers at 48 h post-infection (h p.i.) in CO cells at 25–30 ◦ C. This virus is sensitive to Chloroform, acid and heat treatments while its replication could be inhibited by 5- iodo-2-deoxyuridine (IUDR), which indicating that this virus isolate is lipid membrane containing with a DNA genome. Elec- tron micrographs were shown abundant cytoplasmic icosahedral virons, 120–160 nm in diameter, existed in the virus-infected CO cells. This virus was moderately virulent for turtles in infection tests and there was no relationship between this virus and infec- tious pancreatic necrosis virus (IPNV), grass carp haemorrhagic virus (GCHV), chum salmon virus (CSV) in serology. Iridoviruses are large cytoplasmic DNA viruses that are spe- cific for different insect or vertebrate hosts, as causative agents of serious systemic diseases in modern aquaculture and fish farm- ing. Up to the present, many vertebrate iridoviruses have been identified from various taxonomic classes, such as fish (Langdon et al., 1986; Ahne et al., 1989; Armstrong and Ferguson, 1989; 0168-1702/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.virusres.2007.07.002