Originally published as Genetics Published Articles Ahead of Print on February 1, 2008.

Genetics, Vol. 178, 703-709, February 2008, Copyright © 2008
doi:10.1534/genetics.107.079103

The Saccharomyces cerevisiae Homolog of p24 Is Essential for Maintaining the Association of p150^Glued With the Dynactin Complex

I. Alexandra Amaro^*, Michael Costanzo, Charles Boone and Tim C. Huffaker^*,1

^* Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853 and Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Canada M5S 3E1

¹ Corresponding author: Department of Molecular Biology and Genetics, 365 Biotechnology Bldg., Cornell University, Ithaca, NY 14853-2703.
E-mail: tch4{at}cornell.edu

Stu1 is the Saccharomyces cerevisiae member of the CLASP family of microtubule plus-end tracking proteins and is essential for spindle formation. A genomewide screen for gene deletions that are lethal in combination with the temperature-sensitive stu1-5 allele identified ldb18. ldb18 cells exhibit defects in spindle orientation similar to those caused by a block in the dynein pathway. Consistent with this observation, ldb18 is synthetic lethal with mutations affecting the Kar9 spindle orientation pathway, but not with those affecting the dynein pathway. We show that Ldb18 is a component of dynactin, a complex required for dynein activity in yeast and mammalian cells. Ldb18 shares modest sequence and structural homology with the mammalian dynactin component p24. It interacts with dynactin proteins in two-hybrid and co-immunoprecipitation assays, and comigrates with them as a 20 S complex during sucrose gradient sedimentation. In ldb18 cells, the interaction between Nip100 (p150^Glued) and Jnm1 (dynamitin) is disrupted, while the interaction between Jnm1 and Arp1 is not affected. These results indicate that p24 is required for attachment of the p150^Glued arm to dynamitin and the remainder of the dynactin complex. The genetic interaction of ldb18 with stu1-5 also supports the notion that dynein/dynactin helps to generate a spindle pole separating force.

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