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Eukaryotic Cell, December 2008, p. 2087-2099, Vol. 7, No. 12
1535-9778/08/$08.00+0     doi:10.1128/EC.00278-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Copy Number Suppressors of the Aspergillus nidulans nimA1 Mitotic Kinase Display Distinctive and Highly Dynamic Cell Cycle-Regulated Locations{triangledown} ,{dagger}

Leena Ukil, Archana Varadaraj, Meera Govindaraghavan, Hui-Lin Liu, and Stephen A. Osmani*

Department of Molecular Genetics, The Ohio State University, Columbus, Ohio

Received 20 August 2008/ Accepted 11 September 2008

The Aspergillus nidulans NIMA kinase is essential for mitosis and is the founding member of the conserved NIMA-related kinase (Nek) family of protein kinases. To gain insight into NIMA function, a copy number suppression screen has been completed that defines three proteins termed MCNA, MCNB, and MCNC (multi-copy-number suppressor of nimA1 A, B, and C). All display a distinctive and dynamic cell cycle-specific distribution. MCNC has weak similarity to Saccharomyces cerevisiae Def1 within a shared CUE-like domain. MCNC, like Def1, is a cytoplasmic protein with slow mobility during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and its deletion causes polarization defects and a small colony phenotype. MCNC enters nuclei during mitosis. In contrast, MCNB is a nuclear protein displaying increased nuclear levels as cells progress through interphase but is lost from nuclei at mitosis. MCNB is highly related to the Schizosaccharomyces pombe forkhead transcription factor Sep1 and is likely a transcriptional activator of nimA. Most surprisingly, MCNA, a protein restricted to the aspergilli and pathogenic systemic dimorphic fungi (the Eurotiomycetes), defines a nuclear body located near nucleoli at the nuclear periphery of G2 nuclei. During progression through mitosis, the MCNA body is excluded from nuclei. Cytoplasmic MCNA bodies then diminish during early stages of interphase, and single MCNA bodies are formed within nuclei as interphase progresses. Three sites of MCNA phosphorylation were mapped and mutated to implicate proline-directed phosphorylation in the equal segregation of MCNA during the cell cycle. The data indicate all three MCN proteins likely have cell cycle functions.

* Corresponding author. Mailing address: Department of Molecular Genetics, The Ohio State University, 804 Riffe Building, 496 W. 12th Avenue, Columbus, OH 43210. Phone: (614) 247-6791. Fax: (614) 247-6845. E-mail: osmani.2{at}osu.edu

{triangledown} Published ahead of print on 17 October 2008.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

Eukaryotic Cell, December 2008, p. 2087-2099, Vol. 7, No. 12
1535-9778/08/$08.00+0     doi:10.1128/EC.00278-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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