Our understanding of cell cycle regulation has accelerated at an amazing pace. These new insights have had a major impact upon our understanding and treatment of cancer. This impact is likely to increase with further understanding of cell cycle control. The NIMA protein kinase plays a pivotal role in regulating the cell cycle in Aspergillus nidulans. Increasing data indicate that NIMA related kinases regulate the cell cycle in humans as well. This grant outlines experiments aimed at furthering our understanding of cell cycle control. New highly conserved proteins that interact with NIMA and cause cell cycle arrest are to be analyzed. The role of NIMA in programmed cell death is to be analyzed and the hypothesis tested that NIMA plays a role in programmed cell death by promoting DNA condensation. The hypothesis that phosphorylation of histone H3 is essential for DNA condensation at mitosis is to be tested in A. nidulans. We will also test the hypothesis that NIMA is the kinase that phosphorylates histone H3 at mitosis. If NIMA is not the H3 kinase then this kinase will be isolated and its regulation by NIMA studied as mitotic H3 phosphorylation is dependent upon NIMA and is promoted by NIMA. The hypothesis that NIMA promotes DNA condensation by interacting or controlling condensin is also to be tested. Previous work has demonstrated that tyrosine phosphorylation of MPF is a highly conserved mechanism to prevent premature mitosis. However, other levels of checkpoint control over mitotic initiation do exist because A. nidulans strains unable to tyrosine phosphorylate MPF progress normally through the cell cycle and also arrest mitotic initiation if DNA replication is stopped. To isolate additional regulatory functions we plan genetic screens that will isolate new regulators of mitosis that do not function through tyrosine phosphorylation of MPF but may regulate NIMA. Preliminary studies indicate that during mitosis NIMA localizes first to the DNA, then the spindle and finally to the spindle pole body. Experiments are outlined to define the localization of NIMA in fixed and live cells and to define domains within NIMA that are responsible for its cell cycle specific localization and degradation. Finally, the ability of nuclear NIMA to promote translocation of MPF to the nucleus will be tested.
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