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Gene Review

KAR9  -  Kar9p

Saccharomyces cerevisiae S288c

Synonyms: Cortical protein KAR9, Karyogamy protein KAR9, YPL269W
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Disease relevance of KAR9


High impact information on KAR9


Biological context of KAR9

  • In the absence of KAR9, dynein-dependent spindle oscillations are evident before anaphase onset, as are postanaphase dynein-dependent pulling forces that exceed the velocity of wild-type spindle elongation threefold [5].
  • In mitotic cells, GFP-Kar9p localized to a cortical dot with both mother-daughter asymmetry and cell cycle dependence [6].
  • Two phosphorylation sites in Kar9p were previously identified [7].
  • During mitosis in the yeast Saccharomyces cerevisiae, Kar9p directs one spindle pole body (SPB) toward the incipient daughter cell by linking the associated set of cytoplasmic microtubules (cMTs) to the polarized actin network on the bud cortex [7].
  • Moreover, additive phenotypes in bud6Delta kar9Delta or bud6Delta dyn1Delta mutants underscored the separate contributions of Bud6p, Kar9p, and dynein to spindle positioning [8].

Anatomical context of KAR9

  • Kar9p is a novel cortical protein required for cytoplasmic microtubule orientation in yeast [6].
  • Kar9p localization was also altered by mutations in four genes, spa2Delta, pea2Delta, bud6Delta, and bni1Delta, required for normal polarization and actin cytoskeleton functions and, of these, bni1Delta affected Kar9p localization most severely [9].
  • Paradoxically, +TIPs such as the EB1 orthologue Bim1 and Kar9 also associate with spindle pole bodies (SPBs), the centrosome equivalent in budding yeast [10].
  • These contacts are eliminated in bud6 delta cells but are proficient in kar9 delta cells [11].

Associations of KAR9 with chemical compounds


Physical interactions of KAR9

  • These experiments demonstrate that the interaction of cytoplasmic microtubules with the Kar9p cortical attachment site requires the microtubule-binding protein Bim1p [12].
  • Here, we show that the CLIP-170 homologue Bik1p binds directly to Kar9p [13].
  • We propose a model in which Kar3p couples depolymerizing microtubule plus ends to the cell cortex and the Bim1p-Kar9p protein complex maintains attachment during microtubule polymerization [14].

Enzymatic interactions of KAR9

  • Kar9p is hypophosphorylated in bik1delta mutants, and Bik1p binds to both phosphorylated and unphosphorylated isoforms of Kar9p [13].

Regulatory relationships of KAR9

  • The Cyclin-dependent Kinase Cdc28p Regulates Multiple Aspects of Kar9p Function in Yeast [7].
  • Together, these data suggest that Bik1p promotes the phosphorylation of Kar9p on serine 496, which affects its asymmetric localization to one SPB and associated cytoplasmic MTs [13].

Other interactions of KAR9


Analytical, diagnostic and therapeutic context of KAR9


  1. The Bud14p-Glc7p complex functions as a cortical regulator of dynein in budding yeast. Knaus, M., Cameroni, E., Pedruzzi, I., Tatchell, K., De Virgilio, C., Peter, M. EMBO J. (2005) [Pubmed]
  2. Asymmetric loading of Kar9 onto spindle poles and microtubules ensures proper spindle alignment. Liakopoulos, D., Kusch, J., Grava, S., Vogel, J., Barral, Y. Cell (2003) [Pubmed]
  3. Myosin V orientates the mitotic spindle in yeast. Yin, H., Pruyne, D., Huffaker, T.C., Bretscher, A. Nature (2000) [Pubmed]
  4. Molecular linkage underlying microtubule orientation toward cortical sites in yeast. Korinek, W.S., Copeland, M.J., Chaudhuri, A., Chant, J. Science (2000) [Pubmed]
  5. Dynamic positioning of mitotic spindles in yeast: role of microtubule motors and cortical determinants. Yeh, E., Yang, C., Chin, E., Maddox, P., Salmon, E.D., Lew, D.J., Bloom, K. Mol. Biol. Cell (2000) [Pubmed]
  6. Kar9p is a novel cortical protein required for cytoplasmic microtubule orientation in yeast. Miller, R.K., Rose, M.D. J. Cell Biol. (1998) [Pubmed]
  7. The Cyclin-dependent Kinase Cdc28p Regulates Multiple Aspects of Kar9p Function in Yeast. Moore, J.K., Miller, R.K. Mol. Biol. Cell (2007) [Pubmed]
  8. Differential contribution of Bud6p and Kar9p to microtubule capture and spindle orientation in S. cerevisiae. Huisman, S.M., Bales, O.A., Bertrand, M., Smeets, M.F., Reed, S.I., Segal, M. J. Cell Biol. (2004) [Pubmed]
  9. The cortical localization of the microtubule orientation protein, Kar9p, is dependent upon actin and proteins required for polarization. Miller, R.K., Matheos, D., Rose, M.D. J. Cell Biol. (1999) [Pubmed]
  10. {gamma}-Tubulin Is Required for Proper Recruitment and Assembly of Kar9-Bim1 Complexes in Budding Yeast. Cuschieri, L., Miller, R., Vogel, J. Mol. Biol. Cell (2006) [Pubmed]
  11. Kar9p-independent microtubule capture at Bud6p cortical sites primes spindle polarity before bud emergence in Saccharomyces cerevisiae. Segal, M., Bloom, K., Reed, S.I. Mol. Biol. Cell (2002) [Pubmed]
  12. Bim1p/Yeb1p mediates the Kar9p-dependent cortical attachment of cytoplasmic microtubules. Miller, R.K., Cheng, S.C., Rose, M.D. Mol. Biol. Cell (2000) [Pubmed]
  13. The CLIP-170 homologue Bik1p promotes the phosphorylation and asymmetric localization of Kar9p. Moore, J.K., D'Silva, S., Miller, R.K. Mol. Biol. Cell (2006) [Pubmed]
  14. The minus end-directed motor Kar3 is required for coupling dynamic microtubule plus ends to the cortical shmoo tip in budding yeast. Maddox, P.S., Stemple, J.K., Satterwhite, L., Salmon, E.D., Bloom, K. Curr. Biol. (2003) [Pubmed]
  15. The role of the proteins Kar9 and Myo2 in orienting the mitotic spindle of budding yeast. Beach, D.L., Thibodeaux, J., Maddox, P., Yeh, E., Bloom, K. Curr. Biol. (2000) [Pubmed]
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