The Saccharomyces cerevisiae homolog of p24 is essential for maintaining the association of p150Glued with the dynactin complex

Stu1 is the S. cerevisiae member of the CLASP family of microtubule plus-end tracking proteins and is essential for spindle formation. A genome-wide 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 co-migrates with them as a 20 S complex during sucrose gradient sedimentation. In ldb18 cells, the interaction between Nip100 (p150Glued) and Jnm1 (dynamitin) is disrupted, while the interaction between Jmn1 and Arp1 is not affected. These results indicate that p24 is required for attachment of the p150Glued 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.

Key Words: CLASP, S. cerevisiae, dynactin, p24, spindle orientation

Online ISS 1091-6490
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