MOLECULAR CHARACTERIZATION OF BETA-TUBULIN GENES PRESENT IN BENZIMIDAZOLE-RESISTANT POPULATIONS OF HAEMONCHUS-CONTORTUS

A beta-tubulin isotype 1 gene, gru-1, from a benzimidazole (BZ)-resist ant population of the nematode parasite, Haemonchus contortus, was clo ned and sequenced. The predicted gene organisation showed 10 exons and 9 introns, one of which was H. contortus specific. Using probes and r estriction sites selected from this sequence, restriction maps were co nstructed from and around beta-tubulin genes of 3 BZ-susceptible and 7 BZ-resistant populations. There was a reduction in beta-tubulin isoty pe 1 genes to usually one, in BZ-resistant populations. So, our previo usly reported reduction of beta-tubulin probe-reactive RFLP fragments in resistant populations correlated with the reduction in beta-tubulin isotype 1 genes. The beta-tubulin isotype 1 gene present on the appar ently selected fragment and was not always the same, and the geographi cal origin of the resistant populations indicated independent developm ent rather than geographical spread of the resistant populations. The beta-tubulin genes on the apparently selected fragments were transcrib ed and processed to mRNA using the nematode-specific trans-spliced lea der (SL1). Comparison of the derived amino acid sequence of gru-1, wit h known sequences from a susceptible population, identified 3 mutation s that could be involved in BZ resistance.