Identification of a gene for α-tubulin in Aspergillus nidulans

This paper demonstrates that revertants of temperature-sensitive benA (β-tubulin) mutations in Aspergillus nidulans can be used to identify proteins which interact with β-tubulin. Three benomyl-resistant benA (β-tubulin) mutants of Aspergillus nidulans, BEN 9, BEN 15 and BEN 19, were found to be temperature-sensitive (ts −) for growth. Temperature sensitivity co-segregated with benomyl resistance among the progeny of outcrosses of BEN 9, 15 and 19 to a wild-type strain, FGSC#99, indicating that temperature sensitivity was caused by mutations in the benA gene in these strains. Eighteen revertants to ts + were isolated by selection at the restrictive temperature. Four had back-mutations in the benA gene and fourteen carried extragenic suppressor mutations. Two of the back-mutated strains had β-tubulins which differed from the β-tubulins of their parental strains by one (1 −) or two (2 −) negative charges on two-dimensional gel electrophoresis. Although the β-tubulins of the extragenic suppressor strains were all electrophoretically identical to those of the parental strains, one of the suppressor strains, BEN 9R7, had an electrophoretic abnormality in α1-tubulin (1 +). A heterozygous diploid between this strain and a strain with wild-type α1-tubulin was found to have both wild-type and mutant (1 +) α1-tubulins. This experiment rules out post-translational modification as a possible cause of the α1-tubulin abnormality. Thus the suppressor mutation in BEN 9R7 must be in a structural gene for α1-tubulin. We propose that this gene be designated tubA to denote that it is a gene for α1-tubulin in A. nidulans.