Pu R T, Osmani S A
Weis Center for Research, Geisinger Clinic, Danville, PA 17822-2617.
EMBO J. 1995 Mar 1;14(5):995-1003. doi: 10.1002/j.1460-2075.1995.tb07080.x.
NIMA is a cell cycle regulated protein kinase required, in addition to p34cdc2/cyclin B, for initiation of mitosis in Aspergillus nidulans. Like cyclin B, NIMA accumulates when cells are arrested in G2 and is degraded as cells traverse mitosis. However, it is stable in cells arrested in mitosis. NIMA, and related kinases, have an N-terminal kinase domain and a C-terminal extension. Deletion of the C-terminus does not completely inactivate NIMA kinase activity but does prevent functional complementation of a temperature sensitive mutation of nimA, showing it to be essential for function. Partial C-terminal deletion of NIMA generates a highly toxic kinase although the kinase domain alone is not toxic. Transient induction experiments demonstrate that the partially truncated NIMA is far more stable than the full length NIMA protein which likely accounts for its toxicity. Unlike full length NIMA, the truncated NIMA is not degraded during mitosis and this affects normal mitotic progression. Cells arrested in mitosis with non-degradable NIMA are able to destroy cyclin B, demonstrating that the arrest is not due to stabilization of p34cdc2/cyclin B activity. The data establish that NIMA degradation during mitosis is required for correct mitotic progression in A. nidulans.
NIMA是一种细胞周期调控蛋白激酶，除了p34cdc2/细胞周期蛋白B外，它也是构巢曲霉有丝分裂起始所必需的。与细胞周期蛋白B一样，当细胞停滞在G2期时NIMA会积累，而在细胞进行有丝分裂时会降解。然而，它在停滞于有丝分裂期的细胞中是稳定的。NIMA及相关激酶具有一个N端激酶结构域和一个C端延伸区域。C端缺失并不会使NIMA激酶活性完全丧失，但会阻止对nimA温度敏感突变的功能互补，表明该区域对其功能至关重要。NIMA的部分C端缺失会产生一种剧毒激酶，尽管单独的激酶结构域无毒。瞬时诱导实验表明，部分截短的NIMA比全长NIMA蛋白稳定得多，这可能是其毒性的原因。与全长NIMA不同，截短的NIMA在有丝分裂期间不会降解，这会影响正常的有丝分裂进程。用不可降解的NIMA使细胞停滞在有丝分裂期，这些细胞能够破坏细胞周期蛋白B，这表明停滞并非由于p34cdc2/细胞周期蛋白B活性的稳定所致。这些数据表明，在构巢曲霉中，有丝分裂期间NIMA的降解是正确进行有丝分裂进程所必需的。
