γ-tubulin is a component of the spindle pole body that is essential for microtubule function in Aspergillus nidulans

We have recently discovered that the mipA gene of A. nidulans encodes γ-tubulin, a new member of the tubulin superfamily. To determine the function of γ-tubulin in vivo, we have created a mutation in the mipA gene by integrative transformation, maintained the mutation in a heterokaryon, and determined the phenotype of the mutation in spores produced by the heterokaryon. The mutation is lethal and recessive. It strongly inhibits nuclear division, less strongly inhibits nuclear migration, and, as judged by immunofluorescence microscopy, causes a reduction in the number and length of cytoplasmic microtubules and virtually a complete absence of mitotic apparatus. We conclude that γ-tubulin is essential for microtubule function in general and nuclear division in particular. Immunofluorescence microscopy of wild-type hyphae with affinity-purified, γ-tubulin-specific antibodies reveals that γ-tubulin is a component of interphase and mitotic spindle pole bodies. We propose that γ-tubulin attaches microtubules to the spindle pole body, nucleates microtubule assembly, and establishes microtubule polarity in vivo.