Wu L, Osmani S A, Mirabito P M
Henry Hood Research Program, Weis Center for Research, Pennsylvania State University College of Medicine, Danville, Pennsylvania 17822-2617, USA.
J Cell Biol. 1998 Jun 29;141(7):1575-87. doi: 10.1083/jcb.141.7.1575.
NIMA promotes entry into mitosis in late G2 by some mechanism that is after activation of the Aspergillus nidulans G2 cyclin-dependent kinase, NIMXCDC2/NIMECyclin B. Here we present two independent lines of evidence which indicate that this mechanism involves control of NIMXCDC2/NIMECyclin B localization. First, we found that NIMECyclin B localized to the nucleus and the nucleus-associated organelle, the spindle pole body, in a NIMA-dependent manner. Analysis of cells from asynchronous cultures, synchronous cultures, and cultures arrested in S or G2 showed that NIMECyclin B was predominantly nuclear during interphase, with maximal nuclear accumulation in late G2. NIMXCDC2 colocalized with NIMECyclin B in G2 cells. Although inactivation of NIMA using either the nimA1 or nimA5 temperature-sensitive mutations blocked cells in G2, NIMXCDC2/NIMECyclin B localization was predominantly cytoplasmic rather than nuclear. Second, we found that nimA interacts genetically with sonA, which is a homologue of the yeast nucleocytoplasmic transporter GLE2/RAE1. Mutations in sonA were identified as allele-specific suppressors of nimA1. The sonA1 suppressor alleviated the nuclear division and NIMECyclin B localization defects of nimA1 cells without markedly increasing NIMXCDC2 or NIMA kinase activity. These results indicate that NIMA promotes the nuclear localization of the NIMXCDC2/ NIMECyclin B complex, by a process involving SONA. This mechanism may be involved in coordinating the functions of NIMXCDC2 and NIMA in the regulation of mitosis.
NIMA通过某种机制促进G2晚期进入有丝分裂，该机制发生在构巢曲霉G2期细胞周期蛋白依赖性激酶NIMXCDC2/NIMECyclin B激活之后。在此，我们提供了两条独立的证据线索，表明该机制涉及对NIMXCDC2/NIMECyclin B定位的控制。首先，我们发现NIMECyclin B以NIMA依赖的方式定位于细胞核以及与细胞核相关的细胞器——纺锤极体。对来自异步培养物、同步培养物以及停滞在S期或G2期的培养物中的细胞进行分析表明，NIMECyclin B在间期主要位于细胞核中，在G2晚期细胞核积累达到最大值。NIMXCDC2在G2期细胞中与NIMECyclin B共定位。尽管使用nimA1或nimA5温度敏感突变使NIMA失活会将细胞阻滞在G2期，但NIMXCDC2/NIMECyclin B的定位主要在细胞质而非细胞核中。其次，我们发现nimA与sonA发生遗传相互作用，sonA是酵母核质转运蛋白GLE2/RAE1的同源物。sonA中的突变被鉴定为nimA1的等位基因特异性抑制子。sonA1抑制子缓解了nimA1细胞的核分裂和NIMECyclin B定位缺陷，而没有显著增加NIMXCDC2或NIMA激酶活性。这些结果表明，NIMA通过涉及SONA的过程促进NIMXCDC2/NIMECyclin B复合物的核定位。该机制可能参与协调NIMXCDC2和NIMA在有丝分裂调控中的功能。
