A role for NIMA in the nuclear localization of cyclin B in Aspergillus nidulans.
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.
Wu
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L
Henry Hood Research Program, Weis Center for Research, Pennsylvania State University College of Medicine, Danville, Pennsylvania 17822-2617, USA.
Osmani
S A
SA
Mirabito
P M
PM
D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004271:DNA, Fungal; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D000072380:NIMA-Related Kinase 1; D000072379:NIMA-Related Kinases; D034521:Nuclear Matrix-Associated Proteins; D029543:Nucleocytoplasmic Transport Proteins; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017386:Sequence Homology, Amino Acid
D018797:Cell Cycle Proteins; D019926:Cyclin B; D016213:Cyclins; D004271:DNA, Fungal; D005656:Fungal Proteins; D034521:Nuclear Matrix-Associated Proteins; D029543:Nucleocytoplasmic Transport Proteins; C113374:SONA protein, Emericella nidulans; C075058:NIME protein, Emericella nidulans; D000072380:NIMA-Related Kinase 1; D000072379:NIMA-Related Kinases; C442331:NIMA-related kinase 6; D017346:Protein Serine-Threonine Kinases; D018844:Cyclin-Dependent Kinases