Isolation and characterization of a member of the cysteine-rich gene family from Campoletis sonorensis polydnavirus

The endoparasitic wasp Campoletis sonorensis injects a symbiotic polydnavirus into its host Heliothis virescens. Viral gene expression protects the wasp egg and larva from encapsulation by host haemocytes. Three related C. sonorensis polydnavirus (CsPDV) genes, which are expressed in parasitized H. virescens, have been previously isolated and grouped into a cysteine-rich gene family. In this report, a CsPDV gene encoding an abundant 1.4 kb mRNA expressed in parasitized insects was isolated and mapped to viral segment V (15.2 kb) by Southern blotting and PCR. The VHV1.4 cDNA is 1338 bp long and has an ORF that encodes 322 amino acids with two complete and one partial cysteine moths. Similar to other characterized CsPDV cysteine moths, the VHv1.4 moths are also characterized by six cysteines at conserved positions and variable inter-cysteine amino acids. DNA sequence analyses show that the VHv1.4 gene shares regions of significant identity (73-97%) with the VHv1.1 gene, a member of the cysteine-rich gene family. The VHv1.4 and the VHv1.1 proteins are 62% identical overall; at the N termini including the signal peptide and the N-terminal cysteine moth the identity is greater (90%). Unlike other CsPDV cysteine-rich genes, the VHv1.4 cDNA has two conserved domains (77% identical in nucleotides, 55% identical in amino acids) that presumably result from the duplication of a portion of the gene. The VHV1.4 gene has four introns with splicing sites located at positions similar to VHv1.1 introns. Introns 2 and 3, located in the first and second domains respectively, have greater identity (97%) than the flanking exon sequences (77%). We propose, based on the evidence presented in this paper, that the VHV1.4 gene is a new member of the cysteine-rich polydnavirus gene family.