NUCLEAR DIVISION, NUCLEAR-DISTRIBUTION AND CYTOKINESIS IN FILAMENTOUSFUNGI

Nuclear division, nuclear distribution and cytokinesis are fundamental processes of all eukaryotic organisms, and filamentous fungi, specifi cally Aspergillus nidulans and Neurospora crassa, have provided sophis ticated genetic systems for identification of the genes required for t hese processes. Mutational analyses have led to identification of nove l proteins that have subsequently been found to be conserved component s required for nuclear-specific functions. Formation of the mitotic sp indle in A. nidulans has been shown to be dependent on gamma-tubulin, a central element of all microtubule organizing centres, and two kines in-related proteins. Analysis of A. nidulans mitotic mutants has led t o identification of two important cell-cycle regulators, NIMA and BIME . The NIMA kinase is required for entry into mitosis, and BIME has rec ently been identified as a subunit of an anaphase-promoting complex th at targets cyclins for proteolysis. The microtubule-associated motor p rotein cytoplasmic dynein has been discovered in both A. nidulans and N. crassa, and it has been proposed that it provides motive force for the distribution of nuclei within hyphae. Future studies of nucleus-sp ecific processes in filamentous fungi are likely not only to identify additional novel structural and regulatory proteins, but also lead to an understanding of how the processes of nuclear division, nuclear dis tribution and septation are altered to meet the developmental needs of the organism.