A SINGLE AMINO-ACID SUBSTITUTION IN THE BETA-TUBULIN GENE OF NEUROSPORA CONFERS BOTH CARBENDAZIM RESISTANCE AND DIETHOFENCARB SENSITIVITY

Two MBC-resistant mutants of Neurospora crassa, F914 and F939, were sensitive to diethofencarb at a concentration of 0.1-mu-g/ml, while the wild-type strain and other MBC-resistant mutants showed resistance to diethofencarb at a concentration of 100-mu-g/ml. Genetic analysis suggested that the mutations in these two strains were closely linked to the Bml locus which codes for beta-tubulin. When the wild-type strain was transformed by the cloned beta-tubulin gene of the F914 strain, the transformants showed both MBC resistance and diethofencarb sensitivity. On the other hand, the diethofencarb sensitivity of the F914 strain was cancelled by transformation with the wild-type beta-tubulin gene. DNA sequencing of F914 beta-tubulin revealed that glycine was substituted for glutamic acid at position 198 in the F914 strain. Therefore, a single base change in the beta-tubulin gene was proved to confer both MBC resistance and diethofencarb sensitivity.