Abstract
We have cloned and characterized murine Nek3 (NIMA-related kinase 3), a novel mammalian gene product structurally related to the cell cycle-regulatory kinase NIMA of Aspergillus nidulans. By RNase protection, low levels of Nek3 expression could be detected in all organs examined, regardless of proliferative index. In contrast to Nek1 and Nek2, Nek3 levels were not particularly elevated in either the male or the female germ line. Nek3 levels showed at most marginal variations through the cell cycle, but they were elevated in G0-arrested, quiescent fibroblasts. Furthermore, no cell cycle-dependent changes in Nek3 activity could be detected, and no effects upon cell cycle progression could be observed upon antibody microinjection or overexpression of either wild-type or catalytically inactive Nek3. Finally, Nek3 was found to be a predominantly cytoplasmic enzyme. These data indicate that Nek3 differs from previously characterized Neks with regard to all parameters investigated, including organ specificity of expression, cell cycle dependence of expression and activity, and subcellular localization. Hence, the structural similarity between mammalian Neks may not necessarily be indicative of a common function, and it is possible that some members of this kinase family may perform functions that are not directly related to cell cycle control.
Highlights
Cyclin-dependent kinases (Cdks)1 are well established as key regulators of the eukaryotic cell cycle [1,2,3]
Cloning and Sequencing of a Murine Nek3 cDNA—To isolate the mouse homologue of human Nek3, a mouse brain cDNA library was screened with a human Nek3 cDNA fragment
In A. nidulans, NIMA is an essential gene, and the NIMA kinase appears to be a key regulator of the G2 to M transition
Summary
Cyclin-dependent kinases (Cdks) are well established as key regulators of the eukaryotic cell cycle [1,2,3]. In Aspergillus, lack of NIMA function results in a cell cycle arrest in G2 [6, 7], while overexpression of the nimA gene causes the premature onset of mitotic events, The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) AF093416. Such as depolymerization of cytoplasmic microtubules, formation of abnormal mitotic spindles, and chromatin condensation [4, 8]. We describe the molecular cloning and biochemical characterization of a 56-kDa murine protein kinase, termed mNek, that almost certainly repre-
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