CLONING AND CHARACTERIZATION OF CDNAS ENCODING BETA-TUBULIN FROM DIROFILARIA-IMMITIS AND ONCHOCERCA-VOLVULUS

beta-Tubulin is the target for the benzimidazole anthelmintics. Unfort unately, none of these drugs is clinically useful against adult filari ae. However, beta-tubulin has been shown to be a target for antibody-b ased toxicity to Brugia pahangi. We closed and characterized cDNAs enc oding beta-tubulin from 2 filariae. Dirofilaria immitis and Onchocerca volvulus, to explore possible explanations for benzimidazole insensit ivity among adult filariae and the likelihood that epitopes of beta-tu bulin could be used as antigens for a broad-spectrum filarial vaccine. The proteins predicted by these cDNAs were almost identical to the be ta-tubulin previously reported from B. pahangi but were less similar t o a beta-tubulin cDNA from Onchocerca gibsoni. We cloned the genomic l ocus for the O. volvulus beta-tubulin cDNA and compared its organizati on to the reported genomic loci for beta-tubulin in B. pahangi and O. gibsoni. The comparison reinforces the conclusion that the published O . gibsoni gene is in a different family, possibly the beta 2 family pr eviously described in B. pahangi. The substitution of tyr for phe at p osition 200 of beta-tubulin is associated with benzimidazole resistanc e. All 4 filarial beta-tubulins are predicted to encode phe at this po sition, suggesting that filarial beta-tubulin in not inherently insens itive to the benzimidazoles. A monoclonal antibody that recognizes the COOH terminus of B. pahangi beta-tubulin is lethal to this parasite i n culture. The COOH terminal region is the most variable among the dif ferent isotypes of beta-tubulin and distinguishes mammalian from nemat ode tubulins. This region is highly conserved in 3 of the filarial bet a-tubulins.