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Mol Cell

Title:		Functionally distinct isoforms of Cik1 are differentially regulated by APC/C-mediated proteolysis
Author(s):		Benanti JA; Matyskiela ME; Morgan DO; Toczyski DP;
Address:		"Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94115, USA. jbenanti@cc.ucsf.edu"
Journal Title:		Mol Cell
Year:		2009
Volume:		33
Issue:		5
Page Number:		581 - 590
DOI:		10.1016/j.molcel.2009.01.032
ISSN/ISBN:		1097-4164 (Electronic) 1097-2765 (Print) 1097-2765 (Linking)
Abstract:		"Cik1, in association with the kinesin Kar3, controls both the mitotic spindle and nuclear fusion during mating. Here, we show that there are two Cik1 isoforms, and that the mitotic form includes an N-terminal domain required for ubiquitination by the Anaphase-Promoting Complex/Cyclosome (APC/C). During vegetative growth, Cik1 is expressed during mitosis and regulates the mitotic spindle, allowing for accurate chromosome segregation. After mitosis, APC/C(Cdh1) targets Cik1 for ubiquitin-mediated proteolysis. Upon exposure to the mating pheromone alpha factor, a smaller APC/C-resistant Cik1 isoform is expressed from an alternate transcriptional start site. This shorter Cik1 isoform is stable and cannot be ubiquitinated by APC/C(Cdh1). Moreover, the two Cik1 isoforms are functionally distinct. Cells that express only the long isoform have defects in nuclear fusion, whereas cells expressing only the short isoform have an increased rate of chromosome loss. These results demonstrate a coupling of transcriptional regulation and APC/C-mediated proteolysis"
Keywords:		"Anaphase-Promoting Complex-Cyclosome Cdh1 Proteins Chromosome Segregation Gene Expression Regulation, Fungal Mating Factor Membrane Fusion Microtubule Proteins/genetics/*metabolism Microtubule-Associated Proteins/metabolism *Mitosis/genetics Mutation Pept;"
Notes:		"MedlineBenanti, Jennifer A Matyskiela, Mary E Morgan, David O Toczyski, David P eng R37 GM053270/GM/NIGMS NIH HHS/ GM70539/GM/NIGMS NIH HHS/ P30DK06720/DK/NIDDK NIH HHS/ R01 GM053270/GM/NIGMS NIH HHS/ K99GM085013/GM/NIGMS NIH HHS/ GM053270/GM/NIGMS NIH HHS/ R01 GM070539/GM/NIGMS NIH HHS/ R01 GM070539-07/GM/NIGMS NIH HHS/ T32 CA108462/CA/NCI NIH HHS/ T32CA108462/CA/NCI NIH HHS/ K99 GM085013/GM/NIGMS NIH HHS/ Research Support, N.I.H., Extramural Research Support, U.S. Gov't, Non-P.H.S. 2009/03/17 Mol Cell. 2009 Mar 13; 33(5):581-90. doi: 10.1016/j.molcel.2009.01.032"