Cloning, Sequence Analysis, and Expression of the Major Capsid Protein of the Iridovirus Frog Virus 3

The nucleotide sequence of the gene encoding the major capsid protein (MCP) of frog virus 3 (FV3) has been determined and compared to other iridovirus capsid genes. Nucleotide sequence and S1 nuclease analysis showed that the FV3 MCP gene encoded a transcript of 1452 nucleotides containing a 12 nucleotide AU-rich 5′ nontranslated region (NTR) and a 50-nucleotide 3′ NTR whose terminus was predicted to fold into a hairpin of moderate stability. An open reading frame initiating from the 5′-most AUG codon encoded a protein of 463 amino acids with a predicted molecular weight of 49,860. Expression of the putative FV3 MCP genein vitroconfirmed that it encoded the major capsid protein of FV3 and supported the suggestion that translation initiated at AUG-1. Pairwise amino acid alignments detected a high degree of sequence identity between the FV3 MCP and other iridoviruses. These results indicate that iridoviruses possess an evolutionarily related major capsid protein and provide information useful not only in studies of viral gene expression, but also in characterizing newly isolated iridoviruses.