CHARACTERIZATION OF THE GENE FAMILY ENCODING A HOST-PROTECTIVE ANTIGEN OF THE TAPEWORM TAENIA-OVIS

Genomic structure has been determined for a gene encoding a host-prote ctive antigen of the parasitic platyhelminth Taenia ovis. An incomplet e cDNA, known as 45W, encodes the protective antigen. Southern hybridi sation experiments using 45W cDNA as a probe, revealed that the 45W ge ne was a member of a multigene family. Differential Southern hybridisa tion and rapid amplification of cDNA end (RACE) experiments were used to characterise the related genes, allowing the full-length coding reg ion of the 45W encoded antigen to be determined. The gene family compr ises a minimum of four members per haploid genome with each member sho wing varying degrees of 5' and 3' homology with respect to the 45W cDN A. A close homologue of the 45W gene, designated 45S, differed from 45 W at 11 of 985 nt comprising the full-length mRNA. Sequencing of sever al independent RACE products for both 45W and 45S identified a cDNA wh ich may be a product of homologous recombination between these genes, suggesting that the two genes may be alleles. Homologous recombination in genes which encode a host protective antigen such as 45W would pro vide a mechanism by which antigenic variants could arise.