MOLECULAR ANALYSIS AND CHARACTERIZATION OF THE COCHLIOBOLUS-HETEROSTROPHUS BETA-TUBULIN GENE AND ITS POSSIBLE ROLE IN CONFERRING RESISTANCETO BENOMYL

Cochliobolus heterostrophus Tub1 described here is the first beta-tubu lin gene characterized from a naturally occurring benomyl-resistant as comycete plant pathogen, The gene encodes a protein of 447 amino acids . The coding region of Tub1 is interrupted by three introns, of 116, 5 5, and 56 nt, situated after codons 4, 12, and 53, respectively, As a result of the preference for pyrimidines in the third position of the codons when a choice exists between purines and pyrimidines, codon usa ge in the Tub1 gene is biased, Tub1 shows high homology with beta-tubu lin genes of other ascomycete species, However, Tub1 is exceptional in having Tyr(167), compared with Phe(167), possessed by beta-tubulin ge nes of other ascomycetes sequenced thus far. The Tyr(167) residue has been associated with benomyl resistance in other organisms. In contras t, all other benomyl-implicated residues of Tub1 correspond to sensiti vity, Based on these results, we suggest that benomyl resistance in th e fungus probably is attributed to Tyr(167).