CHARACTERIZATION OF GAMMA-TUBULIN COMPLEXES IN ASPERGILLUS-NIDULANS AND DETECTION OF PUTATIVE GAMMA-TUBULIN INTERACTING PROTEINS

gamma-Tubulin is central to the nucleation of microtubule assembly in vivo. Although it is most obviously located at microtubule organizing centers, it is also found in soluble cytoplasmic complexes. Characteri zing these complexes and identifying proteins that interact with gamma -tubulin in vivo will be necessary if gamma-tubulin function is to be understood fully. We have begun to investigate soluble complexes of ga mma-tubulin in Aspergillus nidulans, the organism in which gamma-tubul in was discovered and in which a great deal of genetic and molecular g enetic analysis of gamma-tubulin has been carried out. We find that ap proximately 32%, of the gamma-tubulin in A. nidulans is soluble. Sucro se density gradients revealed that the soluble gamma-tubulin is in 8-2 0S complexes with little or no monomeric gamma-tubulin present. In the presence of 0.5 M KCl, the average size of the complexes decreased an d a peak was present between 4S and 11S. Cross-linking experiments wit h a zero-length cross-linker suggest that gamma-tubulin in isolated nu clei and in intact hyphae interacts physically with three proteins wit h molecular weights of approximately 105, 95, and 80 kDa. (C) 1997 Wil ey-Liss, Inc.