Two α-tubulin genes of Aspergillus nidulans encode divergent proteins

We have isolated and analyzed the tubA and tubB α-tubulin genes of Aspergillus nidulans. The nucleotide sequences of these genes predict polypeptides of 447 amino acids for tubA and 450 for tubB. The predicted amino acid sequences exhibit 28% divergence between the two polypeptides. This is the second known case of such high divergence between α-tubulins within the same species. The tubB gene is unique in that it codes for an extra glycine residue between what are usually the second and third amino acids. RNA blot analysis demonstrates that the tubA and tubB transcripts are each 1.8 kb long. The level of tubA transcript remains the same throughout the cell cycle. The level of tubB transcript does not change at any particular stage in the cell cycle but increases continuously during spore germination. The tubA gene was previously mapped to linkage group eight, and we have now mapped the tubB gene to linkage group four. Gene disruption in heterokaryons suggests that the phenotypic consequences of disruption are different for the tubA and tubB genes. Molecular disruption of tubA results in a block in nuclear division whereas in tubB it gives rise to abnormal cell and nuclear morphology.