STRUCTURE AND EVOLUTIONARY IMPLICATIONS OF A CYSTEINE-RICH CAMPOLETIS-SONORENSIS POLYDNAVIRUS GENE FAMILY

For successful parasitization, the female Campoletis sonorensis endopa rasitic wasp injects a polydnavirus into its host, Heliothis virescens , during oviposition. Viral gene expression induces immunosuppression and alters development of the host. We report here that three abundant ly expressed genes, VHv1.1, WHv1.0, and WHv1.6, describe a polydnaviru s ''cysteine-rich'' gene family which may be important in inducing the se host manifestations. These genes have a similar primary gene struct ure and their proteins contain cysteine motifs characteristic of snail ion-channel ligands, the omega-conotoxins. Like the omega-conotoxins, the intercysteine amino acid residues are hypervariable with only thr ee identical amino acids in all motifs. The conservation of this domai n in the three viral genes may reflect an important functional role fo r these viral proteins in the parasitization of H. virescens. The thre e genes also contain introns similar in sequence at comparable positio ns in their 5' untransLated leaders and coding sequences. VHv1.1 conta ins two cysteine motifs, and each motif is interrupted by an intron at the same position as in the cysteine motifs of WHv1.0 and WHv1.6. Int ron 2 sequences of WHv1.0 and WHv1.6 are 92% identical, while the imme diately flanking exon sequences encoding the cysteine motifs are only 76% identical. This provides an example of nuclear pre-mRNA introns wh ich are more conserved than flanking exons among members of a gene fam ily.