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Yuichiro Hanyu^1,2, Kumiko K. Imai^1,2,, Yosuke Kawasaki^1,2, Takahiro Nakamura^1,2, Yukinobu Nakaseko², Koji Nagao³, Aya Kokubu³, Masahiro Ebe^1,2, Asuka Fujisawa^1,2, Takeshi Hayashi³, Chikashi Obuse^1,2, and Mitsuhiro Yanagida^1,2,3

¹ CREST Research Project, Japan Science Technology Corporation
² Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan
³ The G0 Cell Unit, Okinawa Institute of Science and Technology Promotion Corporation (OIST), Uruma 904-2234, Japan

Calcium/calmodulin-dependent protein kinase (CaMK) is required for diverse cellular functions, and similar kinases exist in fungi. Although mammalian CaMK kinase (CaMKK) activates CaMK and also evolutionarily-conserved AMP-activated protein kinase (AMPK), CaMKK is yet to be established in yeast. We here report that the fission yeast Schizosaccharomyces pombe Ssp1 kinase, which controls G2/M transition and response to stress, is the putative CaMKK. Ssp1 has a CaM binding domain (CBD) and associates with 14-3-3 proteins as mammalian CaMKK does. Temperature-sensitive ssp1 mutants isolated are defective in the tolerance to limited glucose, and this tolerance requires the conserved stretch present between the kinase domain and CBD. Sds23, multi-copy suppressor for mutants defective in type 1 phosphatase and APC/cyclosome, also suppresses the ssp1 phenotype, and is required for the tolerance to limited glucose. We demonstrate that Sds23 binds to type 2A protein phosphatases (PP2A) and PP2A-related phosphatase Ppe1, and that Sds23 inhibits Ppe1 phosphatase activity. Ssp1 and Ppe1 thus seem to antagonize in utilizing limited glucose. We also show that Ppk9 and Ssp2 are the catalytic subunits of AMPK and AMPK-related kinases, respectively, which bind to common β-(Amk2) and -(Cbs2) subunits.

Present address: Department of Biological Responses, Institute of Virus Research, Kyoto University, Kyoto 606-8501, Japan.

Present address: Faculty of Advanced Life Science, Hokkaido University, Sapporo 001-0021, Japan.

^* Correspondence: yanagida{at}kozo.lif.kyoto-u.ac.jp