Requirement for Bbp1p in the Proper Mitotic Functions of Cdc5p in S. cerevisiae

Chong J. Park¹, Sukgil Song², Thomas H. Giddings Jr.³, Hyeon-Su Ro⁴, Krisada Sakchaisri¹, Jung-Eun Park¹, Yeon-Sun Seong¹, Mark Winey³, and Kyung S. Lee¹^*

¹ Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bldg. 37, Rm. 2D11, Bethesda, MD 20892
² Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bldg. 37, Rm. 2D11, Bethesda, MD 20892, College of Pharmacy, Chungbuk National University, 48 Gaesin-dong, Cheongju, Chungbuk, South Korea
³ Department of Molecular, Cellular, and Developmental Biology, CB 347, University of Colorado, Boulder, CO 80309-0347
⁴ Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bldg. 37, Rm. 2D11, Bethesda, MD 20892, Laboratory of Integrative Biotechnology, Korea Research Institute of Bioscience and Biotechnology, 52 Oun-Dong, Yusong, Taejeon, South Korea

^* Corresponding author. E-mail address: kyunglee{at}pop.nci.nih.gov.

The polo-box domain of the budding yeast polo kinase Cdc5p playsan essential role for targeting the catalytic activity of Cdc5pto spindle pole bodies (SPBs) and cytokinetic neck-filaments.Here we report the isolation of Bbp1p as a polo-box interactingprotein by a yeast two-hybrid screen. Bbp1p localizes to theperiphery of the central plaque of the SPB, and plays an importantrole in SPB duplication. Similarly, Cdc5p localized to the cytoplasmicperiphery of the SPB. In vitro binding studies showed that Cdc5pinteracted with the N-terminal domain of Bbp1p (Bbp1p ${Delta}$ C), butapparently not with Mps2p, a component shown to form a stablecomplex with Bbp1p. In addition, Bbp1p, but likely not Mps2p,was required for proper localization of Cdc5p to the SPB. TheC-terminal coiled-coil domain of Bbp1p (Bbp1p^243-385), whichis crucial for both the homo-dimerization and the SPB localization,could target the localization-defective Cdc5p ${Delta}$ C to the SPB andinduce the release of Cdc14p from the nucleolus. Consistentwith this observation, expression of CDC5 ${Delta}$ C-BBP1^243-385 underCDC5 promoter control partially complemented the cdc5 ${Delta}$ defect.These data suggest that Bbp1p ${Delta}$ C interacts with the polo-box domainof Cdc5p, and this interaction is critical for the subcellularlocalization and mitotic functions of Cdc5p.

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